Build three new mobile endpoints for the Anky iOS app and wire them into the post-write pipeline. The codebase is at /home/kithkui/anky.

## Context

The app has 3 tabs:
1. **Write** — user writes stream-of-consciousness. Before they write, they see a personalized prompt.
2. **Stories** — cuentacuentos (already built)
3. **You** — what anky thinks of the user based on all their writing history

After each write, the server should:
- Generate a personalized next-prompt for the user (async, fire-and-forget)
- Update the user's profile via Honcho (already happening in memory_pipeline)
- Send a silent push notification so the iOS app can pre-fetch the new prompt

## What to build

### 1. Migration: `next_prompts` table and `device_tokens` table
### 2. DB queries in `src/db/queries.rs`
### 3. Handlers in `src/routes/swift.rs` — GET /swift/v2/next-prompt, GET /swift/v2/you, POST /swift/v2/device-token
### 4. Route registration in `src/routes/mod.rs`
### 5. Post-write prompt generation in `src/pipeline/guidance_gen.rs`
### 6. Wire the prompt generation into the post-write pipeline for both short sessions and ankys