feat(desktop): personas-as-events foundation with config pinned at create

[wpfleger96]

Summary

Implements the personas-as-events architecture: defines a new Nostr event kind for persona definitions, adds client-side serialization, a local SQLite retention store for offline boot, migrates existing personas.json entries to events, and pins each agent's spawn config onto its record at create time so editing a template never silently mutates running agents.

Changes

Relay side

• crates/buzz-core/src/kind.rs: Register KIND_PERSONA = 30175 as NIP-33 parameterized replaceable, keyed by (pubkey, kind, d_tag) where d_tag is the plaintext persona slug. Compile-time assertion verifies range membership.
• crates/buzz-relay/src/handlers/ingest.rs: Allowlist kind:30175 under Scope::UsersWrite, mark as global-only (never channel-scoped). New tests verify scope and global-only classification.

Desktop client side

• desktop/src-tauri/src/managed_agents/persona_events.rs (new): Serialize PersonaRecord ↔ kind:30175 event. JSON content body contains display_name, system_prompt, avatar_url, runtime, model, provider, name_pool, env_vars. Publish/fetch functions via relay HTTP API.
• desktop/src-tauri/src/managed_agents/retention.rs (new): SQLite retention store with INSERT OR REPLACE on (kind, pubkey, d_tag) for NIP-33 latest-wins semantics. Pending-sync queue for deferred relay publish. Enables offline boot when relay is unreachable.
• desktop/src-tauri/src/managed_agents/personas.rs: Add load_from_retention helper alongside the existing personas.json read path.
• desktop/src-tauri/src/migration.rs: migrate_personas_to_events runs after identity resolution, signs every retained event with the owner's real keys (no placeholder events). Idempotent via retention-row-exists check (the data is the sentinel). Core logic extracted into migrate_personas_in_dir for unit testing.
• desktop/src-tauri/src/lib.rs: Migration call moved after resolve_persisted_identity so keys are always available. Owner keys cloned from AppState and passed to migration.
• desktop/src-tauri/Cargo.toml: Add rusqlite dependency with bundled feature.

Spawn config pinned to the agent record

• At persona-agent create time, snapshot the persona's system_prompt/model/provider/env_vars plus a content hash onto the ManagedAgentRecord (persona_snapshot in persona_events.rs). New record fields provider and persona_source_version, both #[serde(default)].
• Spawn and deploy read that pinned snapshot off the record, never the live persona (runtime.rs::spawn_agent_child, agents.rs::build_deploy_payload) — a running agent stays on the config it was created with across restarts.
• A persona edit reaches an agent only via delete+respawn, which rewrites the snapshot; an "Out of date"/"Orphaned" drift badge shows in the meantime (build_managed_agent_summary compares the pinned hash vs the persona's current hash).
• Pre-existing records are backfilled once at launch (restore.rs::backfill_persona_snapshots); #[serde(default)] means old managed-agents.json files deserialize cleanly, no migration needed.
• Removes the dead mem/persona engram and the fleet_update.rs self-referential loop.

Key design decisions

1. d-tag: plaintext slug — personas are designed for discovery/sharing, not privacy. HMAC blinding is the wrong threat model (that is for private engrams).
2. Retention-first write strategy — write to local SQLite first (durable copy), then publish to relay opportunistically. Migration succeeds on local write, not relay ack.
3. Duplicate safety — INSERT OR REPLACE keyed on (kind, pubkey, d_tag) in SQLite. NIP-33 replaceable semantics handle relay-side idempotency.
4. Record is authoritative for spawn config — once an agent is created, its ManagedAgentRecord snapshot is the source of truth for spawn/deploy, so template edits never silently mutate running agents.
5. No placeholder events — migration requires resolved keys (always available after identity resolution on desktop). Every retention row is a real signed event that downstream code can parse and verify.
6. Data-is-the-sentinel — idempotency keyed on whether the retention store already holds rows for the owner pubkey. No separate sentinel file needed.