feat: TODOS-aware skills, 2-tier Greptile replies, gitignore fix (#61)

* fix: log non-ENOENT errors in ensureStateDir() instead of silently swallowing

Replace bare catch {} with ENOENT-only silence. Non-ENOENT errors (EACCES,
ENOSPC) are now logged to .gstack/browse-server.log. Includes test for
permission-denied scenario with chmod 444.

* feat: merge TODO.md + TODOS.md into unified backlog with shared format reference

Merge TODO.md (roadmap) and TODOS.md (near-term) into one file organized by
skill/component with P0-P4 priority ordering and Completed section. Add shared
review/TODOS-format.md for canonical format. Add static validation tests.

* feat: add 2-tier Greptile reply system with escalation detection

Add reply templates (Tier 1 friendly, Tier 2 firm), explicit escalation
detection algorithm, and severity re-ranking guidance to greptile-triage.md.

* feat: cross-skill TODOS awareness + Greptile template refs in all skills

/ship Step 5.5: auto-detect completed TODOs, offer reorganization.
/review Step 5.5: cross-reference PR against open TODOs.
/plan-ceo-review, /plan-eng-review: TODOS context in planning.
/retro: Backlog Health metric. /qa: bug TODO context in diff-aware mode.
All Greptile-aware skills now reference reply templates and escalation detection.

* chore: bump version and changelog (v0.3.8)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* docs: update CONTRIBUTING.md for v0.3.8 changes

Clarify test tier cost table (Tier 3 standalone vs combined), add TODOS.md
to "Things to know", mention Greptile triage in ship workflow description.

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

plan-eng-review/SKILL.md

@@ -51,6 +51,7 @@ Before reviewing anything, answer these questions:
 1. **What existing code already partially or fully solves each sub-problem?** Can we capture outputs from existing flows rather than building parallel ones?
 2. **What is the minimum set of changes that achieves the stated goal?** Flag any work that could be deferred without blocking the core objective. Be ruthless about scope creep.
 3. **Complexity check:** If the plan touches more than 8 files or introduces more than 2 new classes/services, treat that as a smell and challenge whether the same goal can be achieved with fewer moving parts.
+4. **TODOS cross-reference:** Read `TODOS.md` if it exists. Are any deferred items blocking this plan? Can any deferred items be bundled into this PR without expanding scope? Does this plan create new work that should be captured as a TODO?
 
 Then ask if I want one of three options:
 1. **SCOPE REDUCTION:** The plan is overbuilt. Propose a minimal version that achieves the core goal, then review that.
@@ -123,7 +124,7 @@ Every plan review MUST produce a "NOT in scope" section listing work that was co
 List existing code/flows that already partially solve sub-problems in this plan, and whether the plan reuses them or unnecessarily rebuilds them.
 
 ### TODOS.md updates
-After all review sections are complete, present each potential TODO as its own individual AskUserQuestion. Never batch TODOs — one per question. Never silently skip this step.
+After all review sections are complete, present each potential TODO as its own individual AskUserQuestion. Never batch TODOs — one per question. Never silently skip this step. Follow the format in `.claude/skills/review/TODOS-format.md`.
 
 For each TODO, describe:
 * **What:** One-line description of the work.

plan-eng-review/SKILL.md.tmpl

@@ -42,6 +42,7 @@ Before reviewing anything, answer these questions:
 1. **What existing code already partially or fully solves each sub-problem?** Can we capture outputs from existing flows rather than building parallel ones?
 2. **What is the minimum set of changes that achieves the stated goal?** Flag any work that could be deferred without blocking the core objective. Be ruthless about scope creep.
 3. **Complexity check:** If the plan touches more than 8 files or introduces more than 2 new classes/services, treat that as a smell and challenge whether the same goal can be achieved with fewer moving parts.
+4. **TODOS cross-reference:** Read `TODOS.md` if it exists. Are any deferred items blocking this plan? Can any deferred items be bundled into this PR without expanding scope? Does this plan create new work that should be captured as a TODO?
 
 Then ask if I want one of three options:
 1. **SCOPE REDUCTION:** The plan is overbuilt. Propose a minimal version that achieves the core goal, then review that.
@@ -114,7 +115,7 @@ Every plan review MUST produce a "NOT in scope" section listing work that was co
 List existing code/flows that already partially solve sub-problems in this plan, and whether the plan reuses them or unnecessarily rebuilds them.
 
 ### TODOS.md updates
-After all review sections are complete, present each potential TODO as its own individual AskUserQuestion. Never batch TODOs — one per question. Never silently skip this step.
+After all review sections are complete, present each potential TODO as its own individual AskUserQuestion. Never batch TODOs — one per question. Never silently skip this step. Follow the format in `.claude/skills/review/TODOS-format.md`.
 
 For each TODO, describe:
 * **What:** One-line description of the work.