fix(core): serialize provision runs with a per-VM lock

[NovusEdge]

Two provision runs against one VM each start apk, and the second dies on the apk database lock with exit 99: Unable to lock database: Resource temporarily unavailable. The TUI guarded against itself in one process, but a CLI stoat up auto-provision, a manual stoat provision, and the TUI did not share that guard.

core.WithProvisionLock(dir, fn) holds an exclusive non-blocking flock on <vm dir>/provision.lock while fn runs. A second run finds the lock held and returns ErrProvisionInProgress without touching the guest. The flock is advisory and released by the kernel on process death, so a lock file left by a crash never blocks the next run.

Every provision path funnels through it:

• core.Apply wraps its body in the lock (used by the TUI, stoat up, stoat apply).
• stoat provision drives sshx.Provision directly, so it takes the lock itself around that call.

A concurrent run is a skip, not an error: the CLI prints ": provision already running" and exits 0 (JSON gets a skipped_reason); the TUI shows a plain toast. The in-process m.provisioning guard stays as the same-process fast path.

Tests: WithProvisionLock serializes and reacquires after release; Apply returns ErrProvisionInProgress when the lock is held, before it reaches ssh. just check and just test pass.

[coderabbitai]

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📥 Commits

Reviewing files that changed from the base of the PR and between 51ba1c6 and 1dfe9cf.

📒 Files selected for processing (8)

• internal/cli/run_access.go
• internal/cli/run_apply.go
• internal/cli/run_vm.go
• internal/core/apply.go
• internal/core/apply_test.go
• internal/core/lock.go
• internal/core/lock_test.go
• internal/tui/app.go

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