Add TODO/FIXME drift checker and fix checker count docs

[advancedresearcharray]

Closes #54
Closes #49

Summary

• Adds checkTodoFixme — warns on unresolved TODO / FIXME markers in scaffold markdown (file + line).
• Registers the checker in drift detection with TODO_FIXME issue code and remediation hint.
• Updates README checker table, CONTRIBUTING checker count, and CHANGELOG [Unreleased].

Test plan

• npm run typecheck && npm test && npm run build

[theDakshJaitly]

Thanks for this, @advancedresearcharray — and welcome! Really nice first contribution. It's clear you studied the existing checkers: the signature, the swallow-on-unreadable try/catch, and the index.ts registration all match the house style exactly, and you reconciled the checker count cleanly (the README table was actually missing tool-config-sync and undercounting — you fixed both and landed at 10). Tests cover all the acceptance criteria, and I ran typecheck / test (169 passing) / build locally — all green.

Approving. I've left a couple of non-blocking notes inline — purely optional follow-ups, nothing that should hold up the merge. Thanks again for picking up a good-first-issue and seeing it through.

[theDakshJaitly]

Non-blocking, just flagging two behaviors of the match for posterity:

• False positives: this matches TODO/FIXME literally anywhere, including inside fenced code blocks or a patterns/*.md that documents the convention (e.g. an example showing // TODO). That's exactly what Add a TODO/FIXME drift checker #54 asked for (warning per occurrence), so it's correct as-is — just noting that code-fence/inline-code skipping could be a nice v2 to cut noise.
• Case-sensitive: only uppercase TODO/FIXME match; todo/Fixme are ignored. That's the conventional marker form, so probably intended — confirming it was a deliberate choice.

(FYI the MARKER_RE.lastIndex = 0 reset per line is a good defensive touch on a reused /g regex.)

[theDakshJaitly]

Tiny cosmetic note: the comment says "scaffold markdown," but scaffoldFiles can include root .cursorrules / .windsurfrules, which aren't markdown. Harmless — the warning message reads fine either way.