feat(product-requirements): introduce PRD and FRD authoring skills - #60

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@plugins/trogonstack-product-requirements/.claude-plugin/plugin.json`:
- Line 3: Update the "description" value in plugin.json so it mentions both
Product Requirements Documents (PRDs) and Functional Requirements Documents
(FRDs) to match the README/marketplace; locate the "description" property in
plugins/trogonstack-product-requirements/.claude-plugin/plugin.json and change
its text from only referencing PRDs to something inclusive like "Skills for
writing and reviewing Product Requirements Documents (PRDs) and Functional
Requirements Documents (FRDs)" ensuring wording matches other metadata entries.

In `@plugins/trogonstack-product-requirements/skills/frd-split/SKILL.md`:
- Around line 82-88: The fenced code block showing the directory tree (the block
containing ".trogonai/project/{projectid}/frd/{parent-slug}/", "index.frd.md",
"{child-1-slug}.frd.md", etc.) lacks a language specifier and triggers MD040;
fix it by adding a language label (e.g., text) after the opening triple
backticks in SKILL.md so the block begins with ```text and leave the tree
contents unchanged.

In `@plugins/trogonstack-product-requirements/skills/frd-write/SKILL.md`:
- Around line 160-181: The markdown fenced code blocks in SKILL.md around the
REQ-CHK-003 examples are unlabeled and trigger markdownlint MD040; update both
fenced blocks that contain the "REQ-CHK-003: Payment Confirmation" good and "Bad
(reject this shape)" examples to include a language identifier (e.g.,
```markdown) at the opening backticks so the blocks become ```markdown ... ```
and ensure the closing backticks remain unchanged; search for the REQ-CHK-003
code examples in the file to locate the exact blocks to modify.

In
`@plugins/trogonstack-product-requirements/skills/prd-business-problem/SKILL.md`:
- Line 93: Several fenced code blocks in SKILL.md use plain ``` markers without
a language tag (e.g., the examples that start with the "## The Problem"
heading), which triggers MD040; update each triple-backtick fence to include a
language identifier (use "markdown" for these prose examples) so they become
```markdown ... ```, and apply the same change to the other affected fence near
the second "## The Problem" instance; search for plain ``` fences around those
headings and replace them with ```markdown to satisfy markdownlint and keep
tooling consistent.

In
`@plugins/trogonstack-product-requirements/skills/prd-current-state/assets/current-state-template.md`:
- Around line 17-20: Add a blank line between the "## Cost of the status quo"
heading and the table to satisfy MD058; locate the heading text "## Cost of the
status quo" and insert one empty line before the table rows starting with "|
Cost | Measure | Source |".

In `@plugins/trogonstack-product-requirements/skills/prd-current-state/SKILL.md`:
- Line 83: Two fenced code blocks around the "How the job gets done today"
examples are missing a language tag (triggers markdownlint MD040); update each
opening triple-backtick fence to include a language (e.g., change ``` to
```markdown) for both example blocks so the fences read ```markdown, keeping the
existing block content unchanged and preserving both occurrences of the "How the
job gets done today" example sections.

In
`@plugins/trogonstack-product-requirements/skills/prd-custom-overview/SKILL.md`:
- Around line 100-121: The two fenced example blocks in SKILL.md (the one
starting with the "Rollout Strategy" heading and the "Misc Notes" block) are
missing language identifiers which triggers MD040; update both opening
triple-backtick fences to include the markdown language tag (```markdown) so the
linter passes and the examples are explicitly marked as Markdown.

In `@plugins/trogonstack-product-requirements/skills/prd-personas/SKILL.md`:
- Line 90: The fenced code blocks in SKILL.md around the headings "## Primary:
Mid-market Account Executive" and "## Primary: Sales user" lack language
identifiers and trigger markdownlint MD040; update the opening triple-backtick
fences for those two examples to include "markdown" (i.e., change ``` to
```markdown) so both example fences are annotated and the linter warning is
resolved.

In
`@plugins/trogonstack-product-requirements/skills/prd-product-description/SKILL.md`:
- Line 100: Two fenced example blocks around the "One-liner" headings are
missing language identifiers and trigger markdownlint MD040; edit the two fenced
code blocks that contain the "## One-liner" examples and change their opening
fences from ``` to ```markdown so both example blocks explicitly declare the
markdown language (apply this to both occurrences noted in the file).
- Line 57: The markdown heading "Boundaries (what the product is NOT**" has
unbalanced emphasis and a missing closing parenthesis; update the text in
SKILL.md so the bold and parentheses are balanced, e.g., change the fragment to
"Boundaries (what the product is NOT)" and wrap the whole label in bold as
"**Boundaries (what the product is NOT)**" so the emphasis and parentheses are
correctly closed.

In `@plugins/trogonstack-product-requirements/skills/prd-review/SKILL.md`:
- Around line 38-46: The fenced filesystem tree in SKILL.md is missing a
language identifier, causing MD040; update the opening fence for the snippet
that shows ".trogonai/project/{projectid}/prd/" to use a language specifier (use
text) so the block becomes "```text" instead of "```" and keep the closing fence
unchanged; locate the snippet in SKILL.md and add the word "text" immediately
after the opening triple backticks.

In
`@plugins/trogonstack-product-requirements/skills/prd-success-metrics/assets/success-metrics-template.md`:
- Around line 6-20: The markdown violates MD058 because the tables are not
surrounded by blank lines; update each section (headers "## Primary outcome
metric", "## Leading indicators", and "## Guardrail metrics (must not regress)")
by inserting a blank line immediately after the heading and another blank line
after the table block so that each table is preceded and followed by an empty
line.

In
`@plugins/trogonstack-product-requirements/skills/prd-success-metrics/SKILL.md`:
- Around line 105-148: The MD040 lint is triggered because the fenced code
blocks in SKILL.md lack a language tag; edit the example fences around the
primary outcome/leading/guardrail/decision rules examples and add "md" to each
opening triple-backtick (i.e., change ``` to ```md) so the examples are
explicitly marked as Markdown and the linter no longer flags MD040.

In
`@plugins/trogonstack-product-requirements/skills/prd-technical-requirements/assets/technical-requirements-template.md`:
- Around line 6-37: The markdown linter MD058 complains because the tables under
the "## Performance" and "## Integrations" sections need surrounding blank
lines; modify the template so there is an empty line before and after each table
block (the Performance table starting under "## Performance" and the
Integrations table under "## Integrations") to satisfy MD058 while preserving
the header and table rows.

In
`@plugins/trogonstack-product-requirements/skills/prd-technical-requirements/SKILL.md`:
- Around line 145-188: Add the language tag "md" to both fenced-code blocks that
start with the "## Performance" headings (the detailed example block and the
"Bad" example block) so they read as ```md ... ```; update the opening backticks
for the first large example and the second "Bad" example to include md to
satisfy the MD040 lint rule and ensure proper rendering.