refactor(hooks): extract shared sync chain executor — core/dispatcher.ts

[yonatangross]

Phase 2 of v8.0.0 Architecture Overhaul

Extract the duplicated sequential-with-short-circuit pattern from 3 sync dispatchers into a shared function.

Before (3 files × ~80 LOC = 240 LOC)

`sync-bash-dispatcher.ts`, `sync-write-edit-dispatcher.ts`, `permission/unified-dispatcher.ts` each implement:

• Sequential hook execution
• Short-circuit on block (`!result.continue`)
• Context accumulation with token budget
• Error isolation per hook

After (1 shared + 3 callers = 60 LOC)

`core/dispatcher.ts`:
```typescript
export function executeSyncChain(
hooks: SyncHookConfig[],
input: HookInput, ctx: HookContext,
options: { name: string; budget?: number }
): HookResult
```

Each dispatcher becomes ~5 lines:
```typescript
export function syncBashDispatcher(input, ctx) {
return executeSyncChain(BASH_HOOKS, input, ctx, { name: 'bash', budget: 800 });
}
```

Impact

• -180 LOC (240 → 60)
• Bug fixes in executor benefit all 3 chains
• New sync dispatchers are trivial to add