fix(#1098): guard generate-claude-md against clobbering hand-crafted files; redirect default to .claude/CLAUDE.md (#1118)

/gsd-new-project wrote a repo-root CLAUDE.md full of broad project docs,
overwriting/diluting a hand-crafted instruction file. --force was parsed but
silently dropped, and nothing guarded an existing non-GSD file.

- Guard: an existing instruction file with no `<!-- GSD:<section>-start` markers
  (hand-crafted) is left untouched; report action:"skipped". --force (now wired
  through CmdGenerateClaudeMdOptions) overwrites intentionally. The marker check
  uses /<!-- GSD:[a-z]+-start/ so a file merely documenting GSD syntax is safe.
- Redirect: the Claude-family default output is now ./.claude/CLAUDE.md (a valid
  auto-loaded project-memory location) instead of repo-root ./CLAUDE.md. Aligned
  across the handler default, config-defaults.manifest.json, buildNewProjectConfig,
  the config template, new-project.md, and cmdGenerateClaudeProfile; advisory
  read-CLAUDE.md hints in plan-phase/quick/profile-user updated. Codex still
  writes AGENTS.md.

Closes #1098

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

src/config.cts

@@ -263,7 +263,7 @@ function buildNewProjectConfig(userChoices: Record<string, unknown>): Record<str
     project_code: null,
     phase_naming: 'sequential',
     agent_skills: {},
-    claude_md_path: './CLAUDE.md',
+    claude_md_path: './.claude/CLAUDE.md',
     plan_review: {
       source_grounding: true,
       source_grounding_authority: 'grep',