F9: smoke checklist + performance budgets in CI

- docs/SMOKE.md: the F9 capability checklist — every carried-over harness
  capability mapped to at least one automated case (test target) or a
  manual probe with its observable, per the PRD acceptance rule.
- scripts/bench.sh: enforces both PRD performance budgets and fails CI on
  a miss — `kigi --version` p95 <= 50ms via hyperfine, and TUI first
  frame <= 300ms measured through the pty harness (real vt100 emulator
  answering terminal queries) via the new scripts/first-frame.scenario.json.
  Local run: p95 10.1ms, first frame 134ms.
- pty harness: StepOutcome gains elapsed_ms (stamped per step by the
  scripted runner) — a leading wait_for_text step's elapsed IS the
  spawn-to-first-paint latency the budget reads.
- CI: new `perf` job (macOS + Linux) building the release binaries and
  running scripts/bench.sh.

scripts/first-frame.scenario.json

@@ -0,0 +1,9 @@
+{
+  "name": "first-frame",
+  "description": "CI perf budget: time from pager spawn to the first painted welcome frame (PRD: <= 300ms).",
+  "terminal": { "rows": 40, "cols": 120, "respond_to_queries": true },
+  "environment": { "env": [ { "key": "KIGI_DISABLE_KEYRING", "value": "1" } ] },
+  "steps": [
+    { "action": "wait_for_text", "text": "Kigi", "timeout_ms": 10000 }
+  ]
+}