chore(watch): finish canon→truecopy rename in WATCH.md template strings

[askalf]

What

Finishes the canon→truecopy rename in the watch output template: WATCH.md header, the by-line link, and the watch-accepted.json deep link + '--force semantics' phrasing (6 display strings, 5 lines).

Why now

The README badge links out to the watch branch; distro traffic tomorrow lands on a page that still opens '# canon marketplace watch'. The askalf/canon links redirect, so this is cosmetic — but it's the last old-name surface in the funnel.

Deliberately NOT changed

• canon-corpus.json (and its comment) — the manifest filename is the on-disk contract with support/marketplace-fetch.mjs and the cached corpus in CI; renaming it is a functional change out of scope here.
• Historical CHANGELOG entries and back-compat references elsewhere in the repo.

Verification

• node --check clean; full suite locally: 133 pass / 4 CI-only skips, 0 fail.
• Takes effect on the next watch dispatch or the Monday 06:17Z cron; no re-run needed tonight (current branch content is accurate, just old-named).

[sprayberry-reviewer]

Automated review from the Sprayberry Labs fleet code reviewer (sprayberry-reviewer bot).

Verdict: clean — no blocking issues found.

What I checked

This PR makes 5 cosmetic string substitutions in support/marketplace-watch.mjs — replacing all remaining canon references with truecopy in:

1. A file-header comment (support/marketplace-watch.mjs:14)
2. An inline comment describing --force semantics (support/marketplace-watch.mjs:23)
3. The # truecopy marketplace watch WATCH.md header string (support/marketplace-watch.mjs:120)
4. The by-line blurb linking to the repo (support/marketplace-watch.mjs:123)
5. The accepted-findings deep link + --force phrasing (support/marketplace-watch.mjs:137)

No logic, no data, no control flow is touched. I verified:

• Deep link target is valid: https://github.com/askalf/truecopy/blob/master/support/watch-accepted.json — watch-accepted.json exists in askalf/truecopy at that path.
• Branch target: the link uses master, which matches baseRefName. ✓
• Scope matches PR description: exactly 5 lines changed, matching the "6 display strings, 5 lines" claim (one line touches two strings). ✓
• Intentional exclusions respected: canon-corpus.json (on-disk contract with support/marketplace-fetch.mjs) is correctly left untouched, per PR description. ✓

What's good

The PR description is precise about what was changed and what was deliberately left alone (canon-corpus.json, historical CHANGELOG entries). That's the right way to scope a rename sweep.

No findings.