Add shared mod state store

[Guffawaffle]

Adds a shared JSON store for durable mod-owned preferences.

Cross-process file locks serialize read-modify-write transactions, preserving unrelated state fields. Callers can retry for the lock or attempt an immediate update. Writes use atomic replacement, and unsupported schema versions reject reads and updates.

The default profile uses community_patch_state.json; custom config profiles use sibling state files. This provides shared storage for features such as local officer-preset ordering.

[Guffawaffle]

The consumer restack review exposed a schema-boundary issue in the shared helper, now corrected at 59f48e2: unsupported future/invalid versions are rejected on both reads and writes, and callbacks cannot remove or alter the reserved version field. Three independent correction lanes passed receipt 36ed6b5f7ab4; the remaining gap is a focused automated version-fixture matrix.