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>

docs/FEATURES.md

@@ -2507,9 +2507,10 @@ Users who run a memory / knowledge-base MCP server (for example, ExoCortex-style
 **Purpose:** Allow projects to store their CLAUDE.md in a non-root location. The `claude_md_path` config key controls where `/gsd-profile-user` and related commands write the generated CLAUDE.md file.
 
 **Requirements:**
-- REQ-CMDPATH-01: `claude_md_path` defaults to `./CLAUDE.md`
+- REQ-CMDPATH-01: `claude_md_path` defaults to `./.claude/CLAUDE.md` (a valid project-scoped memory location; changed from `./CLAUDE.md` in v1.5 per [#1098](https://github.com/open-gsd/gsd-core/issues/1098) so generated content does not pollute a hand-crafted repo-root `CLAUDE.md`)
 - REQ-CMDPATH-02: Profile generation commands read the path from config and write to the specified location
 - REQ-CMDPATH-03: Relative paths are resolved from the project root
+- REQ-CMDPATH-04: `generate-claude-md` never overwrites an existing instruction file that lacks GSD section markers (a hand-crafted file) unless `--force` is passed
 
 **Configuration:** `claude_md_path`