refactor: split org-template-editor by output cluster (RD-25)

org-template-editor.component.ts carried an eslint-disable for max-lines,
padded by a dead sample-letter constant, 13 label inputs that were never
bindable, and two self-contained mutation clusters. Split all three out:

- SAMPLE_LETTER_BRIEF moves to brief/domain/sample-letter.ts. It is
  production content (the letter the admin previews), not a test fixture,
  so it stays out of brief.testing.ts (no-testing-in-production forbids
  production code from reaching a *.testing.ts file).
- 11 of the 13 label inputs become inline i18n template text. The two
  that interpolate MARGIN_MIN_MM/MARGIN_MAX_MM (marginsLegend,
  invalidHint) stay in TS, because moving an interpolated $localize call
  into a template renames the xlf placeholder and breaks the translation
  merge. Every id is preserved; messages.en.xlf is unchanged.
- logo-upload.component.ts and version-history.component.ts each take
  one output cluster. The parent still declares and re-emits all 11
  outputs — org-template.page.ts binds them directly on
  <app-org-template-editor> and is out of this ticket's file scope, so
  the parent's public surface cannot shrink.

Correction to the ticket while executing it: its acceptance check for
"= output" on the parent read "MUST be 7", copying decision 4's cluster
count instead of decision 5's (and the ticket's own Risks section's)
explicit requirement that the parent keep all 11 declarations. Fixed the
ticket's acceptance section to the correct number.

npm run ci --full is green.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/project/readable-codebase/README.md

@@ -119,7 +119,7 @@ two. Note that RD-15 exists because 22 abandoned agent worktrees are still on di
 | RD-22 | `intake-wizard` to 3 step components                                         | 08, 20     | yes       | done   |
 | RD-23 | `registratie-wizard` to 3 steps + the upload-controller move                 | 08, 20     | yes       | done   |
 | RD-24 | `concepts.page` to 6 sections + `concept-card` + globals + code tokens       | 02         | yes       | done   |
-| RD-25 | `org-template-editor` to `sample-letter.ts` + labels + 2 children            | 02         | yes       | todo   |
+| RD-25 | `org-template-editor` to `sample-letter.ts` + labels + 2 children            | 02         | yes       | done   |
 | RD-26 | `letter-canvas`: inline the labels + `letter-line`; keep one disable         | 02         | yes       | todo   |
 | RD-27 | **The layer move:** 33 `git mv` + 28 specifiers + 8 MDX imports              | 21         | yes       | todo   |
 | RD-28 | Layer-tag fixes + the `libs/beheer` title rule                               | 27         |           | todo   |