feat(runtime): observability + no-progress detector (Phase 1) (#13)

Phase 1 of plans/autonomous-survival-bot-prd.md. The bot must always be
able to answer "what am I doing and why am I not doing more?" without
parsing the log stream.

New modules:
- runtime/state.js: pure FSM classifier emitting emergency / working /
  recovering / planning / social / idle from snapshot + reflex context.
- runtime/no-progress.js: sliding-window detector that watches position
  and inventory; when both are unchanged for 60 s+, emits one stable
  reason code from REASONS (waiting_for_day, night_hostile_nearby,
  no_food_source, inventory_full, no_reachable_target, planner_empty,
  awaiting_action_cooldown).
- runtime/viewer.js: optional prismarine-viewer launcher behind
  VIEWER_PORT. Lazy import so the dep is not required by default.

Wiring:
- runtime/bot.js: tick() now computes runtimeState + noProgressReason
  every tick and stamps them on the snapshot along with activeSkill,
  currentMilestone (read from plan.md, cached 30 s), lastResult,
  failuresByCode and lastEscalation.
- runtime/bot.js: dispatchAction records lastResult and lastFailureAt
  for the recovering-state classifier.
- runtime/planner.js: exports isPlannerBusy(), readNextMilestone()
  and planExists() so the runtime can show planning state + current
  milestone without spawning extra Pi calls.
- runtime/config.js: adds VIEWER_PORT support.

TUI:
- tui/tui.tsx: StatusBar gains a state badge, current-skill row,
  milestone row, no-progress reason warning, last-result line with
  ok/fail color, failures-by-class summary and last-escalation age.

Co-authored-by: Yuriy Mayatnikov <mayatnikov@me.com>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/runtime.md

@@ -150,6 +150,31 @@ should only suggest what to do *with the existing tools*. If a deeper
 problem is happening, the failure-tracker (see Self-improvement) will
 file a proposal instead.
 
+## Observability (Phase 1 — survival-bot pivot)
+
+Every STATUS snapshot now carries fields the TUI uses to answer
+"what is the bot doing and why isn't it doing more?" without
+parsing the log stream:
+
+| Field | Meaning |
+|-------|---------|
+| `runtimeState` | finite-state classification: `emergency` / `working` / `recovering` / `planning` / `social` / `idle` (see `runtime/state.js`). |
+| `activeSkill` | current dispatched action label, or the last one if idle. |
+| `currentMilestone` | first uncompleted line from `state/<host>/plan.md` (cached 30 s). |
+| `lastResult` | `{ label, ok, code, detail, ts }` of the most recent dispatched action. |
+| `noProgressReason` | one of `waiting_for_day`, `night_hostile_nearby`, `no_food_source`, `inventory_full`, `no_reachable_target`, `planner_empty`, `awaiting_action_cooldown`, … emitted when position + inventory have not changed for ≥60 s (see `runtime/no-progress.js`). |
+| `failuresByCode` | rolling counts of recent failures grouped by class (`bug` / `timeout` / `feature-gap` / `other`). |
+| `lastEscalation` | `{ ts, ageMs }` of the most recent Pi auto-escalation. |
+| `reflexPaused` | mirror of the local pause flag (so TUI shows the right state immediately). |
+
+### Optional: prismarine-viewer
+
+Set `VIEWER_PORT=<port>` in `.env` to launch
+[`prismarine-viewer`](https://github.com/PrismarineJS/prismarine-viewer)
+in-process. The package is **not** a default dep — install it explicitly
+(`npm i prismarine-viewer`) before enabling. If missing, the runtime
+logs a warning and continues.
+
 ## In-game chat (dialog-only)
 
 As of the Phase 0 survival-bot pivot, MC chat does **not** drive bot