refactor(database): split 5 god modules into domain-scoped files

Five files under `src/main/database/` exceeded 400 LOC by combining
multiple responsibilities. Split along natural fault lines. Zero
behavior change — each original `build*Methods` factory still returns
the same method surface, now via spread of smaller builders.

| Original                          | Split into                          | LOC each       |
|-----------------------------------|-------------------------------------|----------------|
| tasks-crud.ts (640)               | tasks-crud / task-sessions-crud /   | 250 / 252 /    |
|                                   | task-queries                        | 177            |
| agents-hierarchy.ts (487)         | agents-hierarchy / agent-permissions| 350 / 151      |
| company-settings.ts (476)         | company-settings / company-metrics  | 122 / 370      |
| documents.ts (426)                | documents / config-revisions        | 318 / 126      |
| runs.ts (413)                     | runs / run-logs / run-events /      | 245 / 96 /     |
|                                   | cost-entries                        | 82 / 52        |

AppDatabase call sites unchanged:
- db.tasks.saveTask, db.tasks.ensureAgentSession (task-sessions-crud),
  db.tasks.listAgentTasks (task-queries)
- db.agents.getChainOfCommand, db.agents.hasAgentPermission
- db.company.getCompanySettings, db.company.getStandupReport
  (company-metrics)
- db.documentsMod.saveDocument, db.documentsMod.recordConfigRevision
- db.runs.createRun, db.runs.appendRunLog (run-logs),
  db.runs.appendRunEvent (run-events), db.runs.recordCostEntry
  (cost-entries)

`database-base.ts` (449) kept as-is — thin facade where every
pass-through is one line; splitting adds mechanical files without
behavior benefit. Will revisit if it grows further.

Aggregator files (`tasks.ts`, `agents.ts`, `company.ts`) each import
and spread the new sub-builders. No renamed exports.

src/main/database/tasks.ts

@@ -1,6 +1,8 @@
 import type { DatabaseSync } from "node:sqlite";
 import type { ReadAll, Transaction } from "./helpers";
 import { buildTaskCrudMethods } from "./tasks-crud";
+import { buildTaskQueryMethods } from "./task-queries";
+import { buildTaskSessionMethods } from "./task-sessions-crud";
 import { buildTaskStatusMethods } from "./tasks-status";
 
 export function buildTaskMethods(
@@ -14,6 +16,8 @@ export function buildTaskMethods(
 ) {
   return {
     ...buildTaskCrudMethods(getDb, readAll, transaction, deps),
+    ...buildTaskQueryMethods(getDb, readAll, transaction),
+    ...buildTaskSessionMethods(getDb, readAll, transaction),
     ...buildTaskStatusMethods(getDb, readAll, transaction, deps),
   };
 }