feat: deterministic scheduler → real Now/Next/Later (P2 thin slice)

CommiTea now recommends its own next unit of work from the live backlog.

- @commitea/core: `schedule()` — dependency topo-sort with priority +
  estimate tie-breaks, single serial capacity, cycle detection, and
  critical-path marking; `selectFocus()` takes the top three. Pure,
  deterministic; the LLM does none of this. +11 tests (39 in core).
  Client gains `getIssueDependencies`.
- main: reconcile also fetches native issue dependencies for the open
  scope and returns edges.
- renderer: `scheduleFocus()` maps real issues+deps→Now/Next/Later;
  Focus renders scheduler output (fixture fallback when unconfigured).

v0 scope (each a later slice): single serial worker (per-person
capacity #8), point durations (Monte Carlo cone #10), estimate-only
(calibration #5). Verified: 14 e2e green (fixtures) + gated live spec —
the board shows the real 25 open + 9 closed, and Focus picks #2
ChangeSource (critical path) as Now. Screenshots confirmed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/core/src/index.ts

@@ -24,3 +24,12 @@ export type {
 
 export { inferColumnV0, LIFECYCLE_COLUMNS } from './lifecycle/lifecycle-v0.js'
 export type { LifecycleColumn } from './lifecycle/lifecycle-v0.js'
+
+export { DEFAULT_ESTIMATE_DAYS, schedule, selectFocus } from './scheduler/scheduler-v0.js'
+export type {
+  DependencyEdge,
+  Focus,
+  SchedulableIssue,
+  ScheduledItem,
+  SchedulePlan,
+} from './scheduler/scheduler-v0.js'