fix: address tool_result dedup, SDK task ID collision, and doc accuracy

P1: tool_result dedup changed from "first wins" to "last wins"
- claude-client.ts: remove emittedToolResultIds Set, both PostToolUse and
  user message handler emit freely. PostToolUse provides immediate UI feedback;
  user handler's potentially more complete result arrives second.
- route.ts: collectStreamResponse replaces existing contentBlock entry when
  duplicate tool_use_id arrives (last wins for DB persistence).
- ChatView.tsx: onToolResult replaces existing state entry by tool_use_id
  instead of skipping, ensuring most complete result is displayed.

P2: SDK task ID collision risk eliminated
- db.ts: syncSdkTasks now uses full sessionId in task ID
  (`sdk-{fullSessionId}-{index}`) instead of truncated 8-char prefix,
  eliminating cross-session primary key collisions.

P2: Todo ordering stabilized
- db.ts: add sort_order column migration, syncSdkTasks writes array index
  as sort_order. getTasksBySession sorts by sort_order ASC, created_at ASC
  so tasks with identical timestamps maintain insertion order.

P3: Documentation field mapping corrected
- agent-tooling-todo-bridge.md: fix field mapping table — actual implementation
  maps activeForm (not priority) to description column. Updated dedup strategy
  docs from "three-layer skip" to "two-layer last-wins replace".

Lint: fix prefer-const for finalPrompt in claude-client.ts.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/chat/ChatView.tsx

@@ -326,8 +326,14 @@ export function ChatView({ sessionId, initialMessages = [], initialHasMore = fal
             markActive();
             setStreamingToolOutput('');
             setToolResults((prev) => {
-              // Dedup: skip if already received for this tool_use_id
-              if (prev.some(r => r.tool_use_id === res.tool_use_id)) return prev;
+              // Last-wins: if same tool_use_id exists, replace with newer (potentially more complete) result
+              const existingIdx = prev.findIndex(r => r.tool_use_id === res.tool_use_id);
+              if (existingIdx >= 0) {
+                const next = [...prev];
+                next[existingIdx] = res;
+                toolResultsRef.current = next;
+                return next;
+              }
               const next = [...prev, res];
               toolResultsRef.current = next;
               return next;