FN-7932: add per-lane Reviewer and Planning thinking-level overrides

Adds validatorThinkingLevel and planningThinkingLevel task fields so the Reviewer and Planning AI lanes can override reasoning effort independently of the shared task thinkingLevel, with dashboard UI, storage, and runtime fallback wiring.

- Add validatorThinkingLevel and planningThinkingLevel to Task/TaskCreateInput types (packages/core/src/types.ts)
- Persist the new fields in the SQLite schema and store read/write/replication paths (packages/core/src/db.ts, store.ts, mesh-task-replication.ts)
- Wire executor and triage lanes to fall back per-lane thinking level -> task.thinkingLevel -> existing settings/lane fallback (packages/engine/src/executor.ts, triage.ts)
- Add per-lane thinking-level selectors to the ModelSelectorTab UI, alongside the existing thinking-level control (packages/dashboard/app/components/ModelSelectorTab.tsx)
- Expose the new fields through the legacy task API and task-workflow routes (packages/dashboard/app/api/legacy.ts, packages/dashboard/src/routes/register-task-workflow-routes.ts)
- Document the new settings in dashboard-guide.md and settings-reference.md
- Add a minor changeset and unit/integration test coverage for store persistence, routes, UI, and agent-session helpers

Files changed:
 .changeset/per-lane-task-thinking.md               |   7 ++
 docs/dashboard-guide.md                            |   2 +
 docs/settings-reference.md                         |   2 +-
 .../src/__tests__/store-thinking-levels.test.ts    |  43 +++++++
 packages/core/src/db.ts                            |  15 ++-
 packages/core/src/mesh-task-replication.ts         |   4 +
 packages/core/src/store.ts                         |  24 +++-
 packages/core/src/types.ts                         |  12 ++
 packages/dashboard/app/api/legacy.ts               |   2 +
 .../dashboard/app/components/ModelSelectorTab.tsx  | 126 ++++++++++++++++++++-
 .../components/__tests__/ModelSelectorTab.test.tsx |  50 +++++++-
 .../src/__tests__/routes-tasks-ops.test.ts         |  74 ++++++++++++
 .../src/routes/register-task-workflow-routes.ts    |  19 +++-
 .../src/__tests__/agent-session-helpers.test.ts    |  15 +++
 packages/engine/src/executor.ts                    |  16 ++-
 packages/engine/src/triage.ts                      |   8 +-
 16 files changed, 395 insertions(+), 24 deletions(-)

Fusion-Task-Id: FN-7932

Fusion-Task-Lineage: 4202f774-aab9-41d2-86a0-f5277dd0f848

Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai>

packages/dashboard/app/api/legacy.ts

@@ -569,6 +569,8 @@ export function updateTask(
     planningModelProvider?: string | null;
     planningModelId?: string | null;
     thinkingLevel?: string | null;
+    validatorThinkingLevel?: string | null;
+    planningThinkingLevel?: string | null;
     plannerOversightLevel?: "off" | "observe" | "steer" | "autonomous" | null;
     reviewLevel?: number | null;
     executionMode?: "standard" | "fast" | null;