feat: session goals - server-driven goal loop with independent small-model audit (#2148)

Arm the target button in the composer and the next prompt becomes a goal:
the server keeps the session working toward it (idle tick -> small-model
audit -> continuation) until the objective is verifiably complete, blocked,
or out of budget — even with the UI closed.

Server (packages/web/server/lib/session-goal):
- event-driven loop on the global SSE hub; goal state lives in
  session.metadata.openchamber.goal (merge-safe patches, stale-write guard
  by goal id), so it survives restarts and syncs to every client for free
- the small-model audit (objective + last assistant turn only, language
  pinned to the objective) is the sole termination authority; blocked needs
  3 consecutive verdicts, audit outages tolerate one unaudited continuation
  then stop the goal as resumable-blocked
- hard stops: optional token budget, auto-continuation cap (Resume grants a
  fresh allowance), turn errors; user abort pauses the goal instead of
  blocking it, and resuming over an aborted tail nudges immediately
- token accounting as a snapshot of the latest turn (input + cache.read +
  output), goal-relative via a creation baseline and segmented across
  compactions; a compaction summary skips the audit and continues
- continuations reuse the session's own provider/model/agent/variant

UI:
- three-mode target button (arm / disarm / manage dialog), informational
  goal strip with inline pause/resume and an Evaluating indicator, sidebar
  state glyph, objective length counter (2000-char server clamp),
  read-only completed goals
- goal entry points: composer (sessions and drafts), start-new-session-
  from-answer dialog, plan implement dialog (plan content becomes the
  objective), scheduled tasks (Run as goal + budget)
- Settings -> Chat -> Goal: feature toggle + default token budget with
  three-layer parity (web server, client persistence, VS Code bridge);
  VS Code renders goal state but hides the entry points (the loop runs in
  the web server only)

Notifications: per-turn "ready" notifications are suppressed while a goal
is active; settling sends one final notification (desktop, web-push, APNs
generic titles with the session name as body) honoring the completion
toggle. Error/question/permission notifications are untouched.

Docs: user guide (session-goals) in all 9 locales + sidebar entry,
scheduled-tasks cross-reference, server module DOCUMENTATION.md.

packages/ui/src/stores/useUIStore.ts

@@ -574,6 +574,9 @@ interface UIStore {
   showReasoningTraces: boolean;
   sessionRecapEnabled: boolean;
   sessionSuggestionEnabled: boolean;
+  sessionGoalEnabled: boolean;
+  sessionGoalDefaultBudgetEnabled: boolean;
+  sessionGoalDefaultBudget: number;
   collapsibleThinkingBlocks: boolean;
   chatRenderMode: ChatRenderMode;
   activityRenderMode: ActivityRenderMode;
@@ -725,6 +728,9 @@ interface UIStore {
   setShowReasoningTraces: (value: boolean) => void;
   setSessionRecapEnabled: (value: boolean) => void;
   setSessionSuggestionEnabled: (value: boolean) => void;
+  setSessionGoalEnabled: (value: boolean) => void;
+  setSessionGoalDefaultBudgetEnabled: (value: boolean) => void;
+  setSessionGoalDefaultBudget: (value: number) => void;
   setCollapsibleThinkingBlocks: (value: boolean) => void;
   setChatRenderMode: (value: ChatRenderMode) => void;
   setActivityRenderMode: (value: ActivityRenderMode) => void;
@@ -873,6 +879,9 @@ export const useUIStore = create<UIStore>()(
         showReasoningTraces: true,
         sessionRecapEnabled: true,
         sessionSuggestionEnabled: true,
+        sessionGoalEnabled: true,
+        sessionGoalDefaultBudgetEnabled: false,
+        sessionGoalDefaultBudget: 200_000,
         collapsibleThinkingBlocks: true,
         chatRenderMode: 'live',
         activityRenderMode: 'summary',
@@ -1581,6 +1590,18 @@ export const useUIStore = create<UIStore>()(
           set({ sessionSuggestionEnabled: value });
         },
 
+        setSessionGoalEnabled: (value) => {
+          set({ sessionGoalEnabled: value });
+        },
+
+        setSessionGoalDefaultBudgetEnabled: (value) => {
+          set({ sessionGoalDefaultBudgetEnabled: value });
+        },
+
+        setSessionGoalDefaultBudget: (value) => {
+          set({ sessionGoalDefaultBudget: value });
+        },
+
         setCollapsibleThinkingBlocks: (value) => {
           set({ collapsibleThinkingBlocks: value });
         },
@@ -2276,6 +2297,9 @@ export const useUIStore = create<UIStore>()(
           showReasoningTraces: state.showReasoningTraces,
           sessionRecapEnabled: state.sessionRecapEnabled,
           sessionSuggestionEnabled: state.sessionSuggestionEnabled,
+          sessionGoalEnabled: state.sessionGoalEnabled,
+          sessionGoalDefaultBudgetEnabled: state.sessionGoalDefaultBudgetEnabled,
+          sessionGoalDefaultBudget: state.sessionGoalDefaultBudget,
           collapsibleThinkingBlocks: state.collapsibleThinkingBlocks,
           chatRenderMode: state.chatRenderMode,
           activityRenderMode: state.activityRenderMode,