feat(#172): persist solve workflow analysis to issue comments

[admarble]

Summary

• Add "Persist Analysis to Issue Comments" section to /solve skill (all 3 locations) with user prompt and gh issue comment posting logic
• Add parseSolveMarkers() to solve-comment-parser.ts for parsing HTML comment markers (<!-- solve:phases=... -->)
• Add "Solve Comment Detection" section to /spec skill (both locations) so spec reads and uses solve's prior analysis before making its own phase recommendation
• 34 new tests for parser functions, all passing

AC Coverage

AC	Status	Detail
AC-1: Solve prompts "Save this plan?"	MET	AskUserQuestion with Y/N options
AC-2: Posts structured comment with markers	MET	gh issue comment with HTML markers
AC-3: Comment includes phases, flags, reasoning	MET	Full template with Flags table
AC-4: Spec checks for solve comment	MET	New section 4.5 in spec SKILL.md
AC-5: Spec uses solve input (can override)	MET	Override requires documented reasoning
AC-6: Tests for new format	MET	34 tests in solve-comment-parser.test.ts
AC-7: Sync all 3 solve SKILL.md	MET	Verified byte-identical
AC-8: Sync both spec SKILL.md	MET	Verified byte-identical

Test plan

• npx vitest run src/lib/solve-comment-parser.test.ts — 34/34 pass
• npm run build — succeeds
• Full test suite — all pre-existing failures only (timeouts in discoverUntrackedWorktrees, semgrep, tautology-detector-cli)
• Manual: Run /solve 123 and verify prompt appears
• Manual: Confirm with Y, verify structured comment posted to issue
• Manual: Run /spec 123 on issue with solve comment, verify it references the analysis

Fixes #172