refactor(#2128): single-source 23 phase-token re-derivations; sanction 14 context-specific sites

Route 23 literal re-derivations of the canonical phase-number token through
phase-id.cjs `PHASE_NUMBER_TOKEN_SOURCE` (via new RegExp). Each conversion was
proven BYTE-IDENTICAL (old.source === new.source && old.flags === new.flags), so
the runtime regexes are unchanged — zero behavior change by construction.

The remaining 14 phase-token sites are genuine but context-specific and stay
literal with a `// phase-id-owner: <reason>` sanction: dir-name parses whose
dash-continuation semantics differ from extractPhaseToken, and the [A-Za-z]
case-variant / [.-] dot-or-dash separator forms that are not source-byte-equal
to the canonical token.

Scanner (`npm run check:phase-id-drift`) is now green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/roadmap-command-router.cts

@@ -73,6 +73,7 @@ function checkW021(content: string): W021Warning[] {
   // #1729: `(?:\s*\([^)\n]*\))?` tolerates a pre-colon ( ) tag (literal mirror of OPTIONAL_PHASE_TAG_SOURCE).
   const PHASE_RE = /^#{2,4}\s*(?:\[[^\]]+\]\s*)?Phase\s+(\d+)-(\d+)(?:-\d+)*(?:\s*\([^)\n]*\))?\s*:/i;
   // Unprefixed legacy phase heading: ### Phase N: Name  (no hyphen sub-index)
+  // phase-id-owner: UNPREFIXED_PHASE_RE token uses the [A-Za-z] case-variant (identical to the canonical [A-Z] token under /i); kept literal, not source-byte-equal to PHASE_NUMBER_TOKEN_SOURCE.
   const UNPREFIXED_PHASE_RE = /^#{2,4}\s*(?:\[[^\]]+\]\s*)?Phase\s+(\d+[A-Za-z]?(?:\.\d+)*)(?:\s*\([^)\n]*\))?\s*:/i;
 
   let currentMilestoneMajor: number | null = null;