Port the /amicode/traces reader (from stale PR #9) #77

Tracking issue for work stranded on rchari/traces (PR #9, opened 2026-07-09, ~293 commits behind by the time it was closed).

The feature was never landed. Verified against the current default branch:

$ git ls-tree -r --name-only origin/local/amicode | grep -i 'amicode.*trace'
(no matches)

Nothing superseded it — packages/opencode/src/server/amicode/traces.ts simply does not exist on local/amicode.

What PR #9 carried (3 files, +169):

• packages/opencode/src/server/amicode/traces.ts — the reader
• route registration in packages/opencode/src/server/routes/instance/httpapi/server.ts
• packages/opencode/test/server/amicode-traces.test.ts

Related: harmoniqs/amicode#106 (rchari/traces) is the amicode-side counterpart and is still open and green.

Closing PR #9 as stale rather than rebasing it — the branch is far enough behind that a fresh port against current local/amicode is cleaner. Needs an owner.