fix(episode): forward-sync metadata equality trait

[RecursiveIntell]

Scope and dependency

One bounded trait-surface forward-sync from committed Libraries semantic-memory main c77273a808242c8159288ef5cf04a0a50ba6e808: derive PartialEq for EpisodeMeta in src/types.rs, matching the owner's exact derive line. Add tests/episode_meta_trait.rs to exercise equality, inequality after a field change, and unchanged JSON fields. Add its focused test to the pinned paired-root workflow. This draft stacks on semantic-memory draft PR #4 at 591f1cd0f6e18229780328df0c557213391d1901, itself dependent on #3 and #2. No episode bitemporal-query implementation, store migration, wire-version change, merge or activation.

Evidence boundary

The owner source at the named Libraries commit contains the exact EpisodeMeta derive line; the mirror candidate adds that line. The new trait test first failed to compile against the mirror parent because EpisodeMeta lacked PartialEq (E0369 at both equality assertions). Controller-local validation then ran in a disposable paired root using the workflow-pinned Libraries 0b099ec416de60f6adafb182f1d1e83795d05c56 and candidate source/test bytes: one focused trait test; 11 episode_identity tests; all-targets suite (120 library passed, three ignored, plus integration targets); formatting; strict all-targets Clippy; and Cargo package archive/verification. The controller's scratch-lock check reported exactly the paired-root script's declared PolyKV drop. Cargo warned that locked chacha20 v0.10.1 is yanked. These controller-local paired-root results were not an independent reviewer rerun. Hosted paired-root run 36432182179 subsequently completed success at exact PR head a0e28f9c30b7b5dc396eae120de96eab52de8c12 with the same pinned Libraries 0b099ec416de60f6adafb182f1d1e83795d05c56: the library lane passed 120 with three ignored; FK integration passed five; the new trait integration test passed one; and Cargo archived 173 files and compiled package verification. The scratch lock delta check passed. A later hosted paired-root run 36434587563 completed success at updated PR head f2df66bd0001fabf8675e250f3fa3f5a2fbe52de. After packaging, this workflow extracted the generated .crate to a separate temporary directory and ran Cargo metadata plus the full all-targets suite against that extracted package root; its library lane again passed 120 with three ignored and the integration targets passed. This is proof for the generated package artifact, not the raw Git checkout. The existing workflow pin is older than Libraries main and is unchanged.

PartialEq exposes structural value equality; it does not establish canonical episode identity, temporal truth, digest equivalence, or full semantic parity. The standalone checkout still fails Cargo metadata because blake3 inherits a workspace dependency without a workspace root. This PR is not standalone release-readiness proof. If rejected, the proposed rollback is to close this draft or revert its two scoped commits; no rollback has been performed.