fix: harden Synctech Drive sync lifecycle

[danshapiro]

What changed

• Scheduled Synctech SMS Drive syncs now use the daemon's already-open store when run from serve.
• Drive polls create one outer source-level sync_runs row, including zero-selected polls, and fail that run on list/checksum/stability/download/import/checkpoint errors.
• Drive imports now import backup files into the existing source lifecycle instead of creating nested sync runs per downloaded backup.
• Successful Drive polls update checkpoint counts, touch sources.last_sync_at, and recompute conversation stats when files import.
• Scheduled cache rebuild logic is shared by Gmail/IMAP and configured Synctech syncs.

Why

This keeps scheduled Drive sync lifecycle state accurate and avoids duplicate stores/runs that can obscure failures or freshness.

Impact

Configured Drive sync status, freshness, and analytics cache updates should now reflect every poll, including no-op polls and failed polls.

Validation

• go test -tags "fts5 sqlite_vec" ./cmd/msgvault/cmd ./internal/synctechsms ./internal/store
• make testify-helper-check
• go vet -tags "fts5 sqlite_vec" ./...

[roborev-ci]

roborev: Combined Review (2129ac9)

Summary verdict: No Medium, High, or Critical findings to report.

The only reported issue was Low severity and is omitted per the review-combination rules. Security review found no issues.

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Panel: ci_default_security | Synthesis: codex, 7s | Members: codex_default (codex/default, done, 3m57s), codex_security (codex/security, done, 2m36s) | Total: 6m40s

[roborev-ci]

roborev: Combined Review (3e74ca0)

Summary verdict: one medium correctness issue should be addressed before merge.

Medium

• cmd/msgvault/cmd/add_synctech_sms_drive.go:213 — If one Drive backup imports successfully and a later selected backup fails, the function returns before RecomputeConversationStats runs. The successful file is already marked imported, so future retries may skip it and leave denormalized conversation stats stale indefinitely.

  Suggested fix: Recompute stats after each successful file import, or defer a recompute whenever any records/files were imported before returning an error.

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Panel: ci_default_security | Synthesis: codex, 7s | Members: codex_default (codex/default, done, 5m14s), codex_security (codex/security, done, 1m20s) | Total: 6m41s