feat: diagnose data-plane drift separately from readiness

[b-pm]

Summary

Add an opt-in deep integrity probe:

beeper doctor --data

The existing doctor answers whether the selected target is reachable and ready. This adds a separate, non-fatal data-plane diagnosis that reconciles independent API surfaces so "process ready" is not mistaken for "messaging data healthy."

What it checks

• /v1/accounts
• recent chats
• message search
• bridge inventory and bridge-reported accounts
• bridge logins and their account IDs

It reports:

• account IDs visible in chats/bridges/logins but missing from /v1/accounts
• message-search data while chat listing is empty
• connected accounts with no chats
• bridge state claiming active accounts while neither bridge accounts nor login account IDs are exposed
• probe errors separately as unknown rather than fabricating a healthy result

Behavior

• Read-only. It sends no messages and mutates nothing.
• checks.dataIntegrity.state is ok, degraded, or unknown.
• Data-plane degradation does not change the existing process-readiness exit code. This keeps automation from treating a recoverable indexing/data-surface problem as "the server is down."
• --json exposes the evidence counts, account-ID sets, signals, and probe errors for agents/monitoring.

Why

This generalizes a pattern now visible in several reports:

• chats list and contacts list return empty on self-hosted server (data exists in DB) #14: doctor is healthy, message search has data, but chats/contacts are empty
• Server 4.3.152: local-facebook / local-instagram missing from /v1/accounts and /v1/chats, not restarted on boot #38: connected local bridge logins disappear from accounts/chats after restart
• get_accounts does not return iMessage even when iMessage is active and functional desktop-api-js#36: native iMessage chats exist while /v1/accounts omits the account
• feat: make native iMessage discoverable and directly sendable #42: iMessage-specific diagnostics already demonstrate why cross-surface reconciliation is useful

The underlying Desktop/Server bugs still need their own fixes. This PR makes the CLI honest and operationally useful while those defects are investigated.

Tests

Adds unit coverage for:

• healthy agreement across all surfaces
• account-discovery drift
• chat-index drift
• bridge active-account drift
• partial probe failure producing unknown

Fixes #46.

[chatgpt-codex-connector]

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