feat(agent): Enrich breakdown/decompose agent input with full initiative context

Breakdown and decompose agents now receive all existing phases, tasks,
and pages as read-only context so they can plan with awareness of what
already exists instead of operating in a vacuum.

docs/agent.md

@@ -33,7 +33,7 @@
 1. **tRPC procedure** calls `agentManager.spawn(options)`
 2. Manager generates alias (adjective-animal), creates DB record
 3. `AgentProcessManager.createWorktree()` — creates git worktree at `.cw-worktrees/agent/<alias>/`
-4. `file-io.writeInputFiles()` — writes `.cw/input/` with initiative, pages, phase, task as frontmatter
+4. `file-io.writeInputFiles()` — writes `.cw/input/` with assignment files (initiative, pages, phase, task) and read-only context dirs (`context/phases/`, `context/tasks/`)
 5. Provider config builds spawn command via `buildSpawnCommand()`
 6. `spawnDetached()` — launches detached child process with file output redirection
 7. `FileTailer` watches output file, fires `onEvent` and `onRawContent` callbacks

docs/server-api.md

@@ -117,9 +117,9 @@ Each procedure uses `require*Repository(ctx)` helpers that throw `TRPCError(INTE
 | Procedure | Type | Description |
 |-----------|------|-------------|
 | spawnArchitectDiscuss | mutation | Discussion agent |
-| spawnArchitectBreakdown | mutation | Breakdown agent (generates phases) |
+| spawnArchitectBreakdown | mutation | Breakdown agent (generates phases). Passes full initiative context (existing phases, tasks, pages) |
 | spawnArchitectRefine | mutation | Refine agent (generates proposals) |
-| spawnArchitectDecompose | mutation | Decompose agent (generates tasks) |
+| spawnArchitectDecompose | mutation | Decompose agent (generates tasks). Passes full initiative context (sibling phases, tasks, pages) |
 
 ### Dispatch
 | Procedure | Type | Description |