A label's shape refusal lives in one module, and the settings page and MCP read it from there #5566

For: A label made without a name or a six-digit colour reads the same from every door, because every door reads it from one place. Today each sentence below is typed out separately in src/web/pages/settings.ts and src/http/mcp.ts (repo_labels), so the next edit to one door makes them drift. This is the fix pull #5504's reviewer asked for, applied to these words.

Done:

• [ ] A new src/actions/label_words.ts exports these sentences (a const object or small functions, plain data):

- "A label needs a name and a six-digit hex color."

• [ ] Each door (src/web/pages/settings.ts and src/http/mcp.ts (repo_labels)) imports them, and none of these sentences is typed out anywhere else under src/ (grep -rn for each finds only the module).
• [ ] Answers are byte-for-byte unchanged: every existing test passes as it is.
• [ ] A new test/label-words.test.ts triggers one of the refusals through each door and asserts each answers the module's sentence. It fails if a door retypes the words.
• [ ] Before pushing, run test/label-words.test.ts, the tests of each door you touched and bun x tsc --noEmit. A red test elsewhere that main also has is named in the pull, not a reason to stop.

Files: src/actions/label_words.ts (new), the doors named, test/label-words.test.ts. Risk: a pure move; change no wording. Other MCP work edits src/http/mcp.ts in parallel, so keep each edit to the literal's own line.