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-parser.cts

@@ -459,6 +459,7 @@ function getMilestonePhaseFilter(cwd: string, versionOverride?: string | null, p
   // the milestone as a bogus "46-6" id.
   const numericRe = roadmapUsesHyphenedIds
     ? /^0*(\d+(?:-\d{2,})*[A-Za-z]?(?:\.\d+)*)/
+    // phase-id-owner: [A-Za-z] case-variant token (identical under /i); kept literal, not source-byte-equal to the canonical PHASE_NUMBER_TOKEN_SOURCE.
     : /^0*(\d+[A-Za-z]?(?:\.\d+)*)/;
 
   function isDirInMilestone(dirName: string): boolean {