fix(local-agent): unify debug log tag across HTTP and report/sync lines

[jeff-r2026]

Problem

The local-agent debug log mixed two tag formats within a single hook fire:

• HTTP request/response lines (localAgentFetch): [local-agent 2bcf67] — has the local-agent prefix but no agent name, so an HTTP line couldn't be traced to which agent made it.
• report / sync / command result lines: [2bcf67] [codebuddy] — has the agent name but no prefix.

Example (before):

[local-agent 2bcf67] → POST .../api/local-agent/sync
[local-agent 2bcf67] ← 200 OK POST .../api/local-agent/sync
[2bcf67] [codebuddy] sync OK (0 command(s))

Fix

• Add a single localAgentTag(context) helper producing the unified [<id6>] [<tool>].
• Change localAgentFetch / ackCommand to take the built tag (they previously took a bare agentId only to build the tag), so HTTP lines now carry the agent name too.
• Converge all call sites (fetchUserGroups, processCommands, reportAndSyncLocalAgent) onto the helper.

No HTTP semantics or payloads changed — this is log-tag only.

After:

[2bcf67] [codebuddy] → POST .../api/local-agent/sync
[2bcf67] [codebuddy] ← 200 OK [OK] POST .../api/local-agent/sync
[2bcf67] [codebuddy] sync OK (0 command(s))

Test Plan

• npx tsc --noEmit passes
• npx vitest run src/__tests__/local-agent.test.ts — 12/12 pass
• npm run build succeeds
• End-to-end: triggered a real hook-dispatch stop --tool codebuddy against the live backend; all 13 debug.log lines now use the single [2bcf67] [codebuddy] format (verified the old [local-agent 2bcf67] shape is gone).

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