[ophyd-async] Reconnect via connect(force_reconnect=True) + atexit shutdown

**Rewritten** — the `Device.disconnect()` proposal is dropped (0019 L168).

## Scope
- Reconnect = `Device.connect(force_reconnect=True)`. The only disconnect we want is **atexit**, so the connector registers an atexit hook (Giles: "atexit is fine") plus explicit `await connector.shutdown()`.
- `ControllerRunner` (#395) owns lifecycle incl. reconnect, so the connector defers to it.
- (Optional/out-of-scope-first-cut) serve-transports-alongside-embed (decision 9): design the runner so a transport list can be added later — no work required here beyond not precluding it.

## Acceptance
`uv run --locked tox -e pre-commit,type-checking,tests` green.

ADR: 0019
Parent: #388
Blocked by: #399

Start with ADR 0019 and the lifecycle described for ControllerRunner in #395, then inspect the connector and Device.connect entry points. Check the dependency on #399 before starting. Done means force_reconnect=True works, atexit and explicit connector shutdown are handled, and uv run --locked tox -e pre-commit,type-checking,tests is green.

Written by the indexing model from the issue text.