feat(code-habits): forbid referencing gitignored paths from shared surfaces

[amitkot]

Summary

• Extends the plans-and-investigations-location skill with a new "CRITICAL: never reference gitignored paths from shared surfaces" section. The skill already routed personal markdown to .local/<kind>/; this adds the companion rule that gitignored paths must not be cited from issues, PRs, commit messages, committed code/docs, skills, or any other artefact other readers will see.
• Two remediation paths spelled out: promote-to-shared (move into a tracked location, commit, then reference the committed path) or summarise-inline. Internal session surfaces (TodoWrite, live transcript) are explicitly exempted.
• Version bumps: marketplace 1.18.0 -> 1.19.0; code-habits plugin 0.4.0 -> 0.5.0; SKILL.md frontmatter 0.3.0 -> 0.5.0 (skipped 0.4.0 to align with plugin version, per repo convention).

Why

The original skill covered where to put personal-process markdown but not what happens once you cite that gitignored path from a public surface. Recent session: a .local/plans/<slug>.md reference landed in a GitHub issue body, producing a dangling pointer for everyone but the author. The fix had to be inline summarisation after the fact; encoding the rule at the skill level prevents the same shape at reference-creation time. Applies generally to anything git check-ignore flags, not just .local/.

Test plan

• Render SKILL.md and confirm the new section reads cleanly.
• jq the manifests to confirm versions (marketplace 1.19.0, code-habits plugin 0.5.0, SKILL.md 0.5.0).
• Reload the plugin in a real session and trigger the skill by attempting to cite .local/foo.md from a shared surface.

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