[#199] Add PlotLink contentType metadata to OWS New Story flow

[realproject7]

Summary

• Add Fiction/Cartoon content type selector modal to New Story creation flow
• Persist contentType in additive .story.json metadata per story directory
• Show "Cartoon" badge in sidebar for cartoon stories; fiction stories have no badge (default)
• Add POST /api/stories/:name/metadata endpoint to write/update .story.json
• Existing stories default to contentType: "fiction" when .story.json is missing — no migration needed
• Add vitest unit tests for readStoryMeta / writeStoryMeta (7 tests)
• Update CLAUDE.md and generated CLAUDE.md with new endpoint and file structure

Test plan

• npm run typecheck passes
• npm run lint passes (no new warnings)
• npm run test passes (48 tests, including 7 new metadata tests)
• Start npm run app:dev — "+ New Story" opens content type modal
• Selecting Fiction creates session identical to previous behavior (no badge)
• Selecting Cartoon creates session, "Cartoon" badge appears after story directory detected
• Cancel dismisses modal without creating session
• Existing stories without .story.json show as fiction (no badge)
• Terminal, wallet, and publish flows remain unchanged

Closes #199

🤖 Generated with Claude Code

[project7-interns]

Verdict: APPROVE

Summary

This PR implements the #199 contentType flow with a focused additive metadata file, a new Fiction/Cartoon creation selector, and sidebar visibility for cartoon stories. Existing stories default to fiction and the changes avoid terminal/session/wallet/publish internals.

Findings

• No blocking findings.

Decision

Approved. The implementation matches the issue acceptance criteria, keeps the scope narrow, and CI is passing: lint, typecheck, and tests all succeeded.

[realproject7]

@re2 verdict: APPROVE

Reviewed:

• Route ordering: POST /:name/metadata sits correctly between GET /:name and GET /:name/:file. No method or path conflicts with existing routes (/archive, /restore, /:name/:file/publish-status).
• Security: safeName() applied to :name param, contentType strictly validated against "fiction" | "cartoon", story directory existence checked before write.
• readStoryMeta / writeStoryMeta: Robust error handling — malformed JSON, missing file, and unknown contentType values all default to "fiction". Consistent with existing readPublishStatus / writePublishStatus pattern.
• Tests: 7 tests cover all edge cases (missing file, valid values, malformed JSON, unknown value, create, overwrite).
• UI: Modal is clean. contentTypeMap ref correctly bridges the untitled-session phase with the actual story directory creation. Cleanup on destroy handled. Silent .catch(() => {}) on metadata write consistent with codebase conventions.
• Sidebar badge: flex-shrink-0 on badge and count prevents layout overflow. Badge only shown for cartoon (fiction is the unmarked default) — correct UX.
• Backward compatibility: contentType optional in StoryBrowser interface, existing stories default to fiction without migration. .story.json is additive and ignored by v1.0.33 scanner (filters .md only). Meets rollback policy from Operator Gate: confirm webtoon rollout baseline and rollback policy #198.
• CONTENT_TYPES constant added to lib/genres.ts with proper type export.

No issues found.