feat(coder): add TokenScope analyzer and DB persistence module

- analyzeMessages classifies message parts into system/user/assistant/tools/reasoning
- persistTaskBreakdown writes JSONB to tasks table
- Backfills the token-analysis/ module (contract committed earlier)
- 6 unit tests covering classification, tool calls, reasoning tokens

apps/coder/src/services/token-analysis/analyzer.ts

@@ -0,0 +1,60 @@
+// TokenScope analyzer — classifies message parts into category breakdown.
+// Ported from opencode-tokenscope (MIT).
+
+export interface TokenBreakdown {
+  system: number;
+  user: number;
+  assistant: number;
+  tools: number;
+  reasoning: number;
+  total: number;
+}
+
+const CHARS_PER_TOKEN = 4;
+
+function estimateTokens(text: string): number {
+  return Math.ceil(text.length / CHARS_PER_TOKEN);
+}
+
+export function analyzeMessages(parts: any[]): TokenBreakdown {
+  const breakdown: TokenBreakdown = { system: 0, user: 0, assistant: 0, tools: 0, reasoning: 0, total: 0 };
+
+  for (const part of parts) {
+    const role = part.role ?? '';
+    const content = part.content ?? '';
+    const tokens = estimateTokens(content);
+
+    switch (role) {
+      case 'system':
+        breakdown.system += tokens;
+        break;
+      case 'user':
+        breakdown.user += tokens;
+        break;
+      case 'assistant':
+        breakdown.assistant += tokens;
+        if (part.tool_calls) {
+          for (const tc of part.tool_calls) {
+            breakdown.tools += estimateTokens(JSON.stringify(tc));
+          }
+        }
+        break;
+      case 'tool':
+        breakdown.tools += tokens;
+        break;
+      default:
+        breakdown.assistant += tokens;
+    }
+
+    if (part.reasoning_parts) {
+      for (const rp of part.reasoning_parts) {
+        const rTokens = estimateTokens(rp.text ?? '');
+        breakdown.reasoning += rTokens;
+        breakdown.assistant -= rTokens;
+      }
+    }
+  }
+
+  breakdown.total = breakdown.system + breakdown.user + breakdown.assistant + breakdown.tools + breakdown.reasoning;
+  return breakdown;
+}