Add emojis to install output to improve visibility during agent-files installation

[williamthorsen]

Problem

The agents-files install and agents-files uninstall commands emit warning lines (Skipping modified item: …, Warning: no … directory) and success summaries (Installed N items for …, Removed N items, skipped N modified items) at the same visual weight as the surrounding progress output. When something is skipped — for example, because the user has modified an installed file — the warning blends into the stream and is easy to miss.

Example of current output:

Installing for platform: rovodev
  Skipping modified item: scripts/describe-change.sh
  Installed 68 items for rovodev

Context

• All install warnings live in packages/agents/src/commands/install.ts (9 console.warn sites) and uninstall warnings in packages/agents/src/commands/uninstall.ts (2 sites).
• Success summary lines: 2 in install.ts, 2 in uninstall.ts.
• status.ts produces a structured status report (no skip/success semantics) and stays as-is.
• Existing tests do not assert on these specific strings, so the wording is safe to change.

Solution

Apply a minimal two-symbol vocabulary across both commands:

• Prefix ⚠️ to every console.warn line in install.ts and uninstall.ts — both Skipping modified … warnings and Warning: no … directory notices.
• Prefix ✅ to the install/uninstall summary lines (Installed N items for …, Removed N items, skipped N modified items, including the shared-guidance variants).
• Leave section headers (Installing for platform: …), Manifest updated., dry-run lines, and status.ts output unchanged.

Format convention: preserve the existing two-space indent, then emoji + single space + original text.

Example of revised output:

Installing for platform: rovodev
  ⚠️ Skipping modified item: scripts/describe-change.sh
  ✅ Installed 68 items for rovodev

Acceptance criteria

• All console.warn lines in install.ts and uninstall.ts start with ⚠️ after the leading indent.
• All success summary lines (Installed N items … in install.ts, Removed N items, skipped N modified items in uninstall.ts, including the shared-guidance counterparts) start with ✅ after the leading indent.
• Section headers, Manifest updated., and dry-run preview lines are unchanged.
• status.ts output is unchanged.
• New/modified output behavior in this change is covered by tests.