feat: add daily token usage analyzer workflow (#1557)

* feat: add daily token usage analyzer workflow

Adds an agentic workflow that runs daily to mine token-usage.jsonl
from recent workflow runs, compute per-workflow statistics (tokens,
cache rates, costs, model mix), identify optimization opportunities,
and create a summary issue.

The workflow:
- Discovers completed runs from the past 24 hours
- Downloads agent-artifacts and extracts token-usage.jsonl
- Computes per-workflow stats (cache hit rate, I/O ratio, cost)
- Flags inefficiencies (zero cache hits, high I/O ratios)
- Compares with previous reports for historical trends
- Creates a structured issue with progressive disclosure

Gracefully handles missing data since token tracking is a new feature.

Closes #1551

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Update .github/workflows/token-usage-analyzer.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update .github/workflows/token-usage-analyzer.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update .github/workflows/token-usage-analyzer.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update .github/workflows/token-usage-analyzer.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: 3 people

.github/aw/actions-lock.json

@@ -45,6 +45,11 @@
       "version": "v0.64.5",
       "sha": "5d2ebfd87a1a45a8a8323c1a12c01b055730dac5"
     },
+    "github/gh-aw-actions/setup@v0.65.3": {
+      "repo": "github/gh-aw-actions/setup",
+      "version": "v0.65.3",
+      "sha": "6b4da262b8f7e0e253d1ae84f400a843b918a4ab"
+    },
     "github/gh-aw/actions/setup@v0.42.0": {
       "repo": "github/gh-aw/actions/setup",
       "version": "v0.42.0",