agents: report tokens + $ cost on every agent comment

Each run now appends a report to the agent's reply: the tool calls it made plus
input/output token totals and the dollar cost. opencode's --format json emits
per-step `tokens` and `cost` (USD, priced from the model) on step_finish events;
build-activity-log.sh sums them across the run.

- build-activity-log.sh: compute for EVERY agent (not just devs — @pm/@qa also
  call tools and cost money); output a collapsed <details> report (summary line
  shows "N tool calls · in X · out Y · $Z"; body lists the tools + a token/cost
  breakdown). Zero-tool runs get a one-line "$Z · in X · out Y" footer.
- publish.sh: build $activity once (near the top) and append it to every agent's
  reply — @pm plan/finalize, @qa verdict/recommendations, and dev PR comments.
- agent.yml: rename the step accordingly.

Models without pricing (self-hosted ollama) report cost $0.0000.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/agent.yml

@@ -185,7 +185,7 @@ jobs:
           FILES: ${{ steps.imgs.outputs.files }}   # opencode -f image flags (vision agents only)
         run: bash "$SCRIPTS/run-agent.sh"
 
-      - name: Build activity log (tool calls + reasoning) from the event stream
+      - name: Build run report (tool calls + input/output tokens + $ cost) from the event stream
         id: log
         env:
           SCRIPTS: ${{ runner.temp }}/agents-scripts