Consolidate duplicated parseTagList and readAll helpers in the agents package

[williamthorsen]

Problem

parseTagList and readAll are implemented identically across multiple CLI modules in the agents package. parseTagList is duplicated in three modules (kb-add, capture-event, kb-edit); readAll is duplicated in four (those three plus update-jira-ticket). The function bodies are byte-for-byte identical; only the readAll doc comments have drifted. Each duplicate is a maintenance liability: a fix or contract change to one copy silently diverges from the others.

Context

The duplication was surfaced during code review of #766 (the explicit-UTC timestamp change touched the kb-add and capture-event CLIs) but predates that work and is unrelated to it, so it was deferred to its own ticket. The original framing named only those two modules; a fuller scan of the agents package found the helpers spread wider — kb-edit carries both, and update-jira-ticket carries readAll.

The agents package has two shared homes: kb-shared/ for KB-domain helpers (it already holds formatUtcTimestamp, computeAgeDays, and dedupeInOrder) and lib/ for domain-agnostic helpers (type-guards.ts, platform.ts, and similar). KB modules already import from lib/ (for example, capture-event imports isEnoent from lib/type-guards.ts).

This is per-package consolidation (within agents), not cross-package coupling — one copy per package is the healthy target.

Proposed solution

Extract each helper to a single definition and import it at every call site in the agents package. Split by concern: parseTagList is tag-domain with KB-only callers, so it goes to the KB-shared helpers (kb-shared/); readAll is a generic stream reader with a non-KB caller (update-jira-ticket), so it goes to the package's general helpers (lib/), which keeps a non-KB module from depending on a KB-named directory. The single readAll definition adopts the most informative of the drifted doc comments. No behavior change.

Acceptance criteria

Must have

• parseTagList has a single definition under the package's KB-shared helpers (kb-shared/), imported by kb-add, capture-event, and kb-edit.
• readAll has a single definition under the package's general helpers (lib/), imported by kb-add, capture-event, kb-edit, and update-jira-ticket.
• No duplicate copy of either helper remains anywhere in the agents package.
• No behavior change; the existing CLI test suites for all four modules pass.
• The extracted helpers are covered by direct unit tests.