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>

.env.example

@@ -59,3 +59,9 @@ OPERATOR_USERNAMES=
 # --- Optional: Telegram bridge (future skill, not wired yet) ------------------
 # TELEGRAM_BOT_TOKEN=
 # TELEGRAM_OPERATOR_CHAT_ID=
+
+# --- Optional: prismarine-viewer for local visual debugging -------------------
+# Set to a port to launch the in-browser viewer alongside the bot
+# (http://localhost:<port>). Requires `npm i prismarine-viewer` — kept out of
+# the default deps to keep the runtime light. Set to 0 or leave empty to skip.
+VIEWER_PORT=0