chore(#2453): resolve the uniform-router-param conflict and clear the warning floor (#2489)

npx eslint . reported 0 errors, 53 warnings. The floor eroded the signal: a
genuinely new warning had to be spotted against noise, so 'lint is clean' was not
usable as a check. This takes it to zero.

Fifty of the 53 were one category in gsd-core/bin/gsd-tools.cjs — all unused
ARGUMENTS (error x30, cwd x10, raw x7, args x3), never unused variables. They are
the Command Routing Hub's uniform handler signature, function routeX({ args, cwd,
raw, error }), declared identically whether or not a handler uses all four
members. argsIgnorePattern: '^_' is structurally in conflict with that convention:
satisfying it would mean _-prefixing ~50 parameters and making the signature
non-uniform across the table. Option 1 of #2453: disable args checking for that
file only, keeping varsIgnorePattern intact so genuinely dead variables (the #2379
class) still surface — verified by injecting an unused variable, which still warns.

This is the config decision #732 explicitly deferred ('Severities stay warn (no
config change in this pass)').

The remaining three predate the issue's count of 51 and are real defects, not
suppressions:

- tests/workflow-compat.test.cjs — the step-9 lookahead used (?=\*\*10\.|\z).
  \z is a Perl/Ruby end-of-input anchor with NO meaning in JavaScript; it matched
  a literal 'z', so the lazy span silently stopped at the first z whenever **10.
  was absent, truncating the captured step and letting the assertion pass against
  a partial block. Corrected to $.
- tests/debugger-prevention.test.cjs — an unused RegExp built one line above the
  one actually used. Removed.
- tests/installer-migrations.test.cjs — try/finally inside a test body, which
  CONTRIBUTING prohibits ('verbose, masks test failures, not an approved
  pattern'); the unused t was the symptom. Converted to t.after().

Closes #2453

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

tests/debugger-prevention.test.cjs

@@ -96,7 +96,6 @@ describe('prevention / blameless-postmortem output (#1963, epic #1957 Phase 3B)'
       const content = fs.readFileSync(AGENT, 'utf8');
       const requiredFields = ['Date', 'Error patterns', 'Root cause', 'Fix', 'Files changed', 'Why not caught', 'Recurrence guard'];
       for (const field of requiredFields) {
-        const re = new RegExp(`\\*\\*${field}`, 'i');
         const matches = content.match(new RegExp(`\\*\\*${field}`, 'gi'));
         assert.ok(
           matches && matches.length >= 2,