Meter awake time and storage: per app and environment, the two quantities a forge charges for #505

Cost and revenue both start from what was used. The runtime already knows when an environment starts, sleeps and wakes; nothing records it.

Acceptance:

• [ ] a meter ledger in bun:sqlite: one row per awake interval (repo, env, placement owned|cloud, started, ended) closed on sleep, stop or shutdown; an interval open at boot is closed at the last heartbeat, never left running
• [ ] storage sampled hourly: bytes of each app's FORGE_APP_DATA and its repository, one row per sample
• [ ] src/core/meter.ts reads: awake seconds and GB-hours per app for a [from, to) range, units stated in the doc comment (seconds; bytes × hours / 1e9)
• [ ] tests: start/sleep/wake/stop produce intervals whose sum matches a hand count; a restart closes the open interval; storage of a fixture directory matches its byte count

Files: new src/core/meter.ts, src/apps/runtime.ts (state transitions), src/core/schema.ts.

Part of the profit slider (#392); the shape is docs/PROFIT.md.

Parked by the crew: the check failed ("the fork flow > a mirror whose git is not ready yet is fetched again, and lands") and the decider saw no point in another try (pull #518 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.