Implement Sophia MVP stages 4-7 (introspection, queries, persistence, polish)

Brings the system from "engrams cluster + form synapses" to a complete
end-to-end demo: ingest text, watch it cluster, ask questions, restart
with state intact.

- Stage 4: birth introspection (taxonomy/goals/open_questions via LLM,
  bounded by the global parallel-op semaphore), per-engram memory log,
  click-to-inspect side panel.
- Stage 5: queries as conversations. POST /api/galaxy/:id/query embeds
  the question, materializes a pinned Query-Engram at the donut center,
  runs broadcast retrieval (global cosine scan + 1-hop synaptic
  expansion with attenuation) and fans out responder LLM calls. The
  integrator runs every 2s on accumulated snippets and streams the
  refining answer back over SSE; responders briefly transition to
  Conversing on the WS bus so the right dots light up.
- Stage 6: snapshot persistence. sled-backed store keyed by galaxy id,
  JSON-encoded values (bincode chokes on internally-tagged enums like
  Manifest/MemoryKind), 60s periodic snapshot task, hydrate-on-boot,
  DELETE /api/galaxy/:id wired through. State survives kill -9.
- Stage 7: HUD additions (sim ticks/sec, LLM queue depth, FPS) via a
  new GET /api/stats polled at 1Hz. `sophia demo` subcommand boots the
  server then auto-ingests a 50-paragraph corpus baked into the binary
  with include_str!. README quickstart added.

Token caps for query_responder/integrator bumped (gemma-4-e4b is a
thinking model — output budget must cover hidden reasoning + visible
answer, otherwise content comes back empty). Pinned engrams skip
physics; their tick scheduling is also skipped at materialization so
they stay perfectly still at the donut center.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Cargo.toml

@@ -56,11 +56,19 @@ rand              = { version = "0.8", features = ["small_rng"] }
 
 # Async helpers
 futures-util      = { version = "0.3", default-features = false, features = ["std", "sink"] }
+tokio-stream      = { version = "0.1", features = ["sync"] }
 bytes             = "1"
 
 # Config
 toml              = "0.8"
 
+# Persistence (Stage 6) — embedded KV with serde_json-encoded values. We
+# pick JSON over bincode because `Manifest` and `MemoryKind` are
+# internally-tagged enums (`#[serde(tag = "kind")]`), which require a
+# self-describing format on the wire. Snapshots are 60-second cadence;
+# JSON's verbosity isn't a real cost at MVP scale.
+sled              = "0.34"
+
 [profile.release]
 lto       = "thin"
 codegen-units = 1