fix(state): throttle repeated VACUUM rewrites (salvage #67351)

[kshitijk4poor]

Salvages #67351 by @nkreadly07 — both commits cherry-picked to preserve authorship, retargeted onto current main (the original branch was ~3.9K commits behind and its hermes_cli/config.py hunk targeted DEFAULT_CONFIG before it moved to hermes_cli/config_defaults.py in 1fe0611).

Context — what this fixes, for whom

Users with sessions.auto_prune: true and a large state.db pay a repeated startup stall: once a prune frees any rows (pruned > 0), main's gate (if vacuum and pruned > 0: — hermes_state.py:8574) runs a full VACUUM on every maintenance sweep. On a multi-GB DB with FTS5 shadow tables, VACUUM holds an exclusive lock for the entire rewrite — seconds per 100MB, so tens of seconds of blocked writes at CLI/gateway startup, repeating day after day even though a recent VACUUM already reclaimed the space.

What the fix does (from #67351, kept verbatim)

• Adds min_vacuum_interval_days (default 30) to maybe_auto_prune_and_vacuum: after a successful VACUUM, stamps last_vacuum in state_meta; subsequent sweeps skip VACUUM until the interval elapses. Pruning itself keeps its normal cadence — SQLite reuses freed pages meanwhile.
• Failed VACUUM does not stamp, so the next sweep retries (test-covered).
• Corrupt last_vacuum meta falls through to "vacuum due" (test-covered).
• Wired through both production callers (cli.py _run_state_db_auto_maintenance, gateway/run.py maintenance hook), config default, and EN+zh docs.

Retargeting done in this salvage (no behavior change vs the original)

• Config default moved to hermes_cli/config_defaults.py (where DEFAULT_CONFIG lives now); verified hermes_cli.config.DEFAULT_CONFIG re-export picks it up.
• Test and docs hunks re-applied against current main text.

Verification

• tests/test_hermes_state.py + tests/test_session_vacuum_config.py: 146 passed on current main (includes the PR's 4 throttle tests: success-stamp, recent-skip, interval-expiry retry, failed-vacuum retry — plus the config-default and CLI-forwarding tests)
• Mutation check: reverting hermes_state.py to main makes all 4 throttle tests fail; restoring goes green
• ruff clean on all changed files
• Attribution: contributor mapping for @nkreadly07 landed via chore: add contributor email mapping for nkreadly07 #76837

Closes #67351 (superseded by this salvage — original author credited via cherry-pick authorship).