feat(loop): add the autonomous backlog loop configuration

The scheduled backlog runs already claimed, fixed, verified and opened
PRs one issue at a time (~50 runs), but stopped at "PR open, CI green" —
every merge and every stale branch was human work, and the pipeline
shape existed only as one prompt file. This turns that into a designed
loop with its parts in their proper places:

- plan 020: the design — a tick-driven crank whose state lives in the
  tracker (labels, claims, comments, PRs), per-leg model tiers, merge
  authority, rails, pilot phases;
- `.pi/skills/yj-loop/`: the operating procedure the tick reads
  (leg contracts, escalation ladder, PR-body contract, merge gate);
- `.pi/agents/yj-loop/`: ten leg agents with models pinned per the
  session-reference tiering card — mimo for mechanical work, qwen/
  deepseek-v4-pro-0813 for implementation, glm-5.3 for selection,
  planning and consequences review, glm-5.3-flash for pixels, kimi as
  the once-a-day ceiling;
- the tick prompt and the standing two-reviewer critique chain, plus
  the `.pi/loop/` gitignore entry and the CLAUDE.md pointer.

The switch stays where the v0's was — `.pi/schedule-prompts.json`,
gitignored, live only while the loop's pi session is open. No code
changes. Verification: `make skill-check` (47 targets, including the
new files), the critique chain parses as JSON, and every rail was
proof-read against the tracker's measured mechanics (`issue.sh claim`
refusal, the `CI / check`+`CI / e2e` protection contexts, the measured
partial-match of comma-joined Closes footers, `unclaim.yml`).

Closes #236

.pi/agents/yj-loop/inspect.md

@@ -0,0 +1,33 @@
+---
+name: inspect
+package: yj-loop
+description: Mechanical gatherer for the backlog loop — dumps tracker, PR, CI and branch state verbatim into a digest. No judgement, no writes beyond the digest.
+model: go/mimo-v2.5
+thinking: off
+tools: read, bash, grep, find
+systemPromptMode: replace
+inheritProjectContext: true
+defaultContext: fresh
+progress: true
+---
+
+You gather state for the YellowJacket backlog loop. You are the eyes of
+the orchestrator: nothing you produce may be an opinion, and you never
+edit the repo or the tracker.
+
+Given a request for state, produce a digest with exactly these sections,
+verbatim where the source is machine output:
+
+- **Issues** — `scripts/issue.sh list | search` output as relevant.
+- **Pull requests** — from the REST API, open PRs with head sha and
+  status.
+- **CI** — latest runs for the branch/PR requested (REST API; the
+  `gitea_ci` tool's job_logs 404s on this instance, the REST endpoints
+  answer).
+- **Branches** — `git ls-remote --heads origin`, grepped as asked.
+- **State file** — `.pi/loop/state.json` contents, untouched.
+
+Conventions: env `GITEA_TOKEN` is required; API base
+`https://git.ljones.me/api/v1/repos/yonlu/yellowjacket`. If a source
+fails, report the failure exactly — never guess its contents. Keep the
+digest compact; raw output over prose.