fix: persist review gate config outside transient state

[fscfede-beep]

Summary

Fixes #684.

• move durable workspace config to CODEX_HOME/plugin-cc/config/<workspace>.json
• keep job state under the existing CLAUDE_PLUGIN_DATA / temp roots
• make getConfig() prefer the durable config while retaining the existing state config as a legacy fallback
• mirror setConfig() into the current legacy state for compatibility
• use the same workspace slug/hash for durable config and transient state

This removes CLAUDE_PLUGIN_DATA from the authority boundary for stopReviewGate, so Setup and Stop can run with different plugin-data environments without silently disagreeing about whether the gate is enabled.

Validation

Windows 11 / Node 26.3.1:

• test-first reproduction on main: enable under plugin-data root A, read under root B -> false (fail-open)
• after the patch the same A→B read stays true, and disabling under B is observed under A
• end-to-end integration: Setup enables the gate under root A; Stop runs under root B with the same CODEX_HOME and correctly returns a blocking review decision
• targeted Stop/setup integration: 3 passed, 0 failed
• state regression: 4 passed, 0 failed
• node --check plugins/codex/scripts/lib/state.mjs
• git diff --check

[chatgpt-codex-connector]

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[sylvesterkaczmarek]

Moving stopReviewGate out of transient plugin state fixes the authority boundary: Setup and Stop may legitimately run with different CLAUDE_PLUGIN_DATA, but the workspace policy must remain the same. Reusing one canonical workspace key for both paths avoids a second identity scheme, and preferring durable config while mirroring legacy state gives a reasonable compatibility transition. The cross-root integration test pins the actual fail-open bug rather than only the storage helper.