Add autter doctor end-to-end setup validation command

[sagnik11]

What

New autter doctor command: one-command setup validation that answers "is autter actually capturing and attributing right now?" — including validating a real checkpoint event end-to-end (checkpoint → daemon → working log → commit → attribution).

Requested by Alan and Kanka (and implicitly Mayank): a doctor/validation command to identify missing hooks, invalid configuration, and service/connectivity failures. Built as a focused presentation layer over the existing diagnostics.rs + install-hooks installer primitives rather than a new check framework.

Checks

Section	Checks
Setup	git binary + minimum version (configured and terminal git), config-file parse, repository allow/exclude eligibility
Background service	daemon readiness + real trace2 ingestion probe (auto-starts/restarts stale daemons)
Git capture (trace2)	trace2 global config for both gits, trace2 file self-check
End-to-end checkpoint	real human/mock_known_human/mock_ai checkpoints in a scratch repo, committed, attribution verified via blame — skipped with a pointer when the service check already failed
AI agent hooks	per-agent installed/up-to-date status from the install-hooks installers; VS Code ≥ 1.109.3 native-hooks chain (hook file + chat.useHooks + chat.hookFilesLocations) refactored out of debug.rs for reuse; undetected agents collapse to one line
Account & sync	auth state — an expired session fails loudly since sync silently no-ops when unauthenticated; API reachability probe (only when authenticated, so it never fires in tests/air-gapped local-only use)

UX / contract

• One ✓ / ⚠ / ✗ / - line per check; every failure gets a concrete fix: line (failure details + command logs stay available in autter debug).
• Exit code: 0 when no check fails (warnings allowed), 1 otherwise — unlike autter debug, which stays a full always-exit-0 support dump.
• --json: stable single-line machine-readable report (checks[], summary, ok) for CI/scripts.
• --skip-trace2-checks mirrors the debug flag (the file self-check briefly rewrites global git config).
• Broken-install error paths (suggest_autter_debug) now point users at autter doctor; shared remediation strings updated likewise.

Why the config-file check matters

The runtime load path silently falls back to defaults when ~/.autter/config.json is malformed — a typo disables every setting with zero signal. Doctor is now the place that failure mode becomes visible (it reuses the error-propagating load_file_config_public() path).

Tests

• Unit tests for status mapping, summary counting, and JSON shape.
• Integration tests (tests/integration/doctor.rs): full end-to-end pass — the test writes the trace2 global config autter install would write (pointed at the per-test daemon socket) and asserts the checkpoint round-trip check passes, plus JSON/summary/exit-code consistency, unknown-flag rejection, and --skip-trace2-checks. Connectivity is asserted skipped so tests never touch the network.

Manually smoke-tested in a fully isolated env (HOME/gitconfig/daemon dir): misconfigured trace2 renders the expected failures + fixes; correctly configured env passes the full round-trip; --json and --help verified.

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