feat(hcp): persist session history in Room

[daniele21]

Superseded for integration by #346. This PR is the obsolete stacked HCP-15 branch based on the pre-replay session-contract line. #346 replays only the HCP-15 Room session-history slice onto dev, preserving the already-integrated HCP-14 contract and avoiding stale stacked history. Keep this PR/branch only as historical recovery context until #346 is safely integrated; do not merge, rebase, or continue implementation here.

Original scope:

Implements HCP-15 persistence foundation as a stacked child of session-contract PR #321.

Changes:

• Room telemetry DB v9 with inference_sessions table and generation session_id/use_case_revision/binding_revision columns;
• dedicated session DAO with independent bounded retention;
• Room repository implements SessionTelemetryRepository on the same DB/executor lifecycle;
• session and generation identity mappers;
• 8->9 migration preserving historical runs with nullable new identity;
• mapper and repository retention/query tests.

This still does not switch the phone app composition from in-memory to Room or instrument session lifecycle; those remain HCP-16/phone composition follow-ups.