fix(#2043): reject single-digit slug word in phase-token extraction (all sites)

A phase whose slug's first word is a bare single digit (dir
`46-6-rs-pipeline-orchestrator`, roadmap phase "6 Rs Pipeline Orchestrator" →
slug `6-rs-…`) had its phase token over-collected as `46-6` instead of `46`, so
`gsd-tools` phase-by-number lookups (init.plan-phase, init.phase-op, and
downstream execute/verify/ship) resolved phase_dir=null / has_context=false.

Root cause: an over-broad "looks numeric" test (`/^\d/`, `\d+(?:-\d+)*`)
classified token segments and could not distinguish a legitimate zero-padded
sub-phase segment (`01`, `02`) from a single-digit slug word (`6`). Zero-padded
phase/sub-phase segments are always ≥2 digits, so requiring ≥2 digits is the
structural distinguisher. Applied consistently across every same-class
implementation the triage identified (fixing extractPhaseToken alone leaves the
health-check and milestone-filter subsystems exposed):

- src/phase-id.cts extractPhaseToken — a pure-numeric leading segment continues
  only with ≥2-digit segments; a letter-prefixed milestone id (`M1`) still
  admits its single-digit sub-phase (`M1-2`).
- src/validate.cts PHASE_TOKEN_FROM_DIR_RE (W005/W006/W007 health checks) and
  canonicalPlanStem (I001 plan/summary pairing).
- src/roadmap-parser.cts isDirInMilestone numericRe (getMilestonePhaseFilter —
  highest blast radius: a false negative silently excludes a phase from the
  milestone).
- src/core-utils.cts + its verbatim duplicate src/phase.cts extractCanonicalPlanId.

Regression tests added across tests/{phase-id,health-validation,core-utils,
roadmap-parser}.test.cjs using the shared `46-6-rs-…` fixture, asserting the
token resolves to `46` (not `46-6`) while legit multi-segment tokens
(`01-02`, `02-03-04`, `M1-2`, `68-01`, `02-01`) are unchanged. The
roadmap-parser test exercises the real getMilestonePhaseFilter end-to-end.

The residual ≥2-digit-leading-slug case (e.g. `NN-2024-roadmap`) stays out of
scope — subsumed by the #612 / #565 phase-ID convention work, per the issue.

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

src/roadmap-parser.cts

@@ -469,8 +469,12 @@ function getMilestonePhaseFilter(cwd: string, versionOverride?: string | null, p
   }
 
   const roadmapUsesHyphenedIds = [...normalized].some(n => n.includes('-'));
+  // #2043: milestone-prefixed sub-phase components must be zero-padded (≥2 digits)
+  // — "-\d{2,}" instead of "-0*\d+" — so a single-digit slug word after the phase
+  // number (e.g. dir "46-6-rs-…") captures "46" and is not silently excluded from
+  // the milestone as a bogus "46-6" id.
   const numericRe = roadmapUsesHyphenedIds
-    ? /^0*(\d+(?:-0*\d+)*[A-Za-z]?(?:\.\d+)*)/
+    ? /^0*(\d+(?:-\d{2,})*[A-Za-z]?(?:\.\d+)*)/
     : /^0*(\d+[A-Za-z]?(?:\.\d+)*)/;
 
   function isDirInMilestone(dirName: string): boolean {