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>

runtime/planner.js

@@ -170,3 +170,30 @@ export function stopPlanner() {
 export function readCurrentPlan() {
 	return readOr(PLAN_PATH);
 }
+
+export function isPlannerBusy() {
+	return planInFlight;
+}
+
+// Returns the first uncompleted milestone in plan.md (a line that starts
+// with a list marker but is NOT preceded by "✓ "), or null if the plan is
+// empty or every milestone is done. Plain text, leading list markers
+// stripped, capped at 200 chars to keep it TUI-friendly.
+export function readNextMilestone() {
+	const text = readOr(PLAN_PATH);
+	if (!text.trim()) return null;
+	for (const raw of text.split("\n")) {
+		const line = raw.trim();
+		if (!line) continue;
+		const m = line.match(/^(?:[-*]|\d+[.)])\s+(.*)$/);
+		if (!m) continue;
+		const content = m[1];
+		if (content.startsWith("✓ ") || content.startsWith("[x] ") || content.startsWith("[X] ")) continue;
+		return content.slice(0, 200);
+	}
+	return null;
+}
+
+export function planExists() {
+	return readOr(PLAN_PATH).trim().length > 0;
+}