PBI-56 + ST-1275: PLAN_READY → GRILLING re-grill + SKIPPED status rendering (#147)

* fix(ST-1272): allow PLAN_READY → GRILLING re-grill transition

actions/ideas.ts already lists PLAN_READY in GRILL_TRIGGERABLE_FROM,
but lib/idea-status.ts ALLOWED_TRANSITIONS was missing the
PLAN_READY → GRILLING edge. As a result, clicking Grill on a PLAN_READY
idea returned 422 "Status-transitie ongeldig" while the UI button was
enabled. Mirrors the existing PLANNED → GRILLING re-grill behaviour.

- lib/idea-status.ts: PLAN_READY allows GRILLING in addition to
  PLANNING/PLANNED
- __tests__/lib/idea-status.test.ts: explicit assert for
  PLAN_READY → GRILLING and PLAN_READY added to the regrill loop
  covering every GRILL_TRIGGERABLE_FROM status

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* feat(ST-1275): render SKIPPED job status in chart-colors and insights

Closing the gap left when ClaudeJobStatus.SKIPPED was added to the schema:
the badge map and case-mapper already covered it, but the chart palette,
the per-day insights aggregator and the stacked-bar chart did not. SKIPPED
jobs (e.g. cmovkur8 manually flipped during the no-op-exit hotfix) now
render with a muted style consistent with cancelled.

- lib/chart-colors.ts: JOB_STATUS_COLORS gains a 'skipped' entry
  (var(--muted-foreground), same intensity as cancelled — neither rood/orange)
- lib/insights/agent-throughput.ts: DayCount + STATUSES + perDay zero-fill
  now include 'skipped'; the SQL terminal_7d filter already counted SKIPPED
- app/(app)/insights/components/agent-throughput.tsx: STACKED_STATUSES and
  the empty-state guard include 'skipped'
- __tests__: chart-colors keys list, job-status round-trip ('all 7 statuses')
  and the insights non-zero filter all account for SKIPPED

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

__tests__/lib/insights/agent-throughput.test.ts

@@ -48,7 +48,7 @@ describe('getJobsPerDay', () => {
 
     // All days should have zero counts except the three we seeded
     const nonZero = result.perDay.filter(
-      d => d.done + d.failed + d.queued + d.claimed + d.running + d.cancelled > 0,
+      d => d.done + d.failed + d.queued + d.claimed + d.running + d.cancelled + d.skipped > 0,
     )
     expect(nonZero).toHaveLength(3)