Phase 2c: Approach B reconnect — Tier-0 while linked, Tier-1 while work pending

[itsniper]

Parent: #51

Requirements

• Work-driven connects enable Tier-0 (OS auto-reconnect) while linked.
• Idle teardown / intentional cancel drops Tier-0 (connection cancel).
• Tier-1 ladder armed only while work pending or Advanced hold with reconnect; disarmed when quiet.
• Idle grace: if Tier-0 reconnects with empty work and no hold, cancel again.
• Single ensure-linked path shared with Advanced connect (FR-11.4).

Acceptance criteria

• Tier-0 not left enabled indefinitely after idle with no hold
• Tier-1 does not run with empty work and no hold
• Tests (as far as mocks allow; note Tier-0 auto-reconnect give-up: replace testInjectDisconnect with mock support + on-device verification #40/State-restoration test fidelity: simulate willRestoreState in CoreBluetoothMock (retire actor-boundary-only coverage) #42 limits)
• Behavior documented in DocC / Background