fix(#1437): add phase.list-plans to gsd-tools (#1485)

* fix(#1437): add phase.list-plans to gsd-tools

Register phase.list-plans in PHASE_COMMAND_ALIASES, implement
cmdPhaseListPlans in src/phase.cts (uses findPhaseInternal + scanPhasePlans
to return plan_count/has_plans/plans/phase_dir), and wire the handler in
phase-command-router. Previously every call produced "Unknown phase
subcommand".

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(#1437): register new test file in lint-test-file-count allowlist

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(#1437): rename test to fix-NNN convention; update file-count allowlist

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/lint-test-file-count.allowlist.json

@@ -60,6 +60,7 @@
     },
     "phase": {
       "files": [
+        "fix-1437-phase-list-plans.test.cjs",
         "bug-214-phase-researcher-write-truncation-contract.test.cjs",
         "phase-dependency-levels.test.cjs",
         "phase.test.cjs"