fix(#2136): route operator-facing date fields through local clock day

clock.today() derived the calendar day by slicing a UTC ISO instant
(nowIso().split('T')[0]), so in any negative-UTC-offset zone during UTC's early
hours last_activity named a day the operator had not reached yet — ahead of
last_updated's local date, written by the same call.

- Add Clock.localToday(): host-local YYYY-MM-DD via getMonth/getDate/
  getFullYear, honoring the same GSD_NOW_MS pin as today()/nowIso().
- Route operator-facing date-only fields through localToday(): last_activity
  (state-transition ×7, state.cts), roadmap 'completed <date>' (phase.cts,
  roadmap.cts), milestone completion date (milestone.cts), todo/scaffold
  completion (commands.cts — now threaded through the realClock seam).
- Leave today() (UTC) as the source for internal/cosmetic stamps.

Closes #2136

src/state-transition.cts

@@ -255,7 +255,7 @@ export type ProgressRecord = Record<string, unknown>;
 
 export type StateTransitionDeps = {
   progressProvider: () => ProgressRecord | null;
-  clock: { today: () => string; nowIso: () => string };
+  clock: { today: () => string; localToday: () => string; nowIso: () => string };
   /**
    * Roadmap content provider for transitions that re-derive milestone-wide
    * progress from ROADMAP.md (completePhase). Optional: transitions that don't
@@ -418,7 +418,7 @@ function beginPhaseCore(
       ? `---\n${reconstructFrontmatter(existingFm as unknown as Frontmatter)}\n---\n\n${b}`
       : b;
 
-  const today = deps.clock.today();
+  const today = deps.clock.localToday();
 
   // Consult the field-classification table for the frontmatter keys this
   // transition touches (codex Phase 1 review: "table not consulted by
@@ -721,7 +721,7 @@ function mutateCurrentPositionForAdvance(
  * adapter to construct CLI output.
  */
 function advancePlanCore(content: string, deps: StateTransitionDeps): StateTransitionResult {
-  const today = deps.clock.today();
+  const today = deps.clock.localToday();
 
   // #1255: body-field replacements operate on body only (frontmatter stripped),
   // not on the full content. The YAML `status:` key matches `^Status:\s*`
@@ -849,7 +849,7 @@ function completePhaseCore(
   deps: StateTransitionDeps,
 ): StateTransitionResult {
   const updated: string[] = [];
-  const today = deps.clock.today();
+  const today = deps.clock.localToday();
 
   // Consult the field-classification table for the frontmatter keys this
   // transition touches (same guard beginPhaseCore applies). A missing row is a
@@ -1020,7 +1020,7 @@ function plannedPhaseCore(
   deps: StateTransitionDeps,
 ): StateTransitionResult {
   const updated: string[] = [];
-  const today = deps.clock.today();
+  const today = deps.clock.localToday();
 
   for (const fmKey of ['status', 'last_activity', 'last_activity_desc']) {
     const cls = getFieldClassification(fmKey);
@@ -1124,7 +1124,7 @@ function milestoneSwitchCore(
   intent: { kind: 'milestoneSwitch'; version: string; name: string },
   deps: StateTransitionDeps,
 ): StateTransitionResult {
-  const today = deps.clock.today();
+  const today = deps.clock.localToday();
   const updated: string[] = [
     'milestone',
     'milestone_name',
@@ -1222,7 +1222,7 @@ function milestoneCompleteCore(
   deps: StateTransitionDeps,
 ): StateTransitionResult {
   const updated: string[] = [];
-  const today = deps.clock.today();
+  const today = deps.clock.localToday();
   const version = intent.version;
 
   for (const fmKey of ['status', 'last_activity', 'last_activity_desc']) {
@@ -1520,7 +1520,7 @@ function syncCore(
   intent: { kind: 'sync'; totalPlansInPhase: number | null; percent: number | null },
   deps: StateTransitionDeps,
 ): StateTransitionResult {
-  const today = deps.clock.today();
+  const today = deps.clock.localToday();
   const changes: string[] = [];
   let modified = content;
   const updated: string[] = [];