feat(trace): classify run-state failures as PR check, verification, environment, or tool

[kylerankin]

Trace failures all rendered as a red ✘ that read like the pull request's own
checks going red. A workspace mismatch, an unavailable verification, or a
cancelled review were indistinguishable from a real PR check failure (#465).

Add a TraceClass taxonomy beside the visual SpanStatus: status still says
"failed"; cls says why. classStatus() collapses the four failure classes to
failure and cancelled to skipped, so the icon vocabulary never changes — only
the reason becomes distinct, shown as a badge.

• head_changed (P0 — materialize an isolated exact PR head workspace before executable verification #471) → environment / WORKSPACE, never pr-check
• review_missing/incomplete/unparsable → verification / UNVERIFIED
• mutation_failed → tool / TOOL
• cancelled review or tool call → cancelled / CANCELLED, rendered skipped
• the selected PR's failing checks → pr-check / CHECK on the root span, derived
  from PR state (ciStatus), not the run log

classifyRunState/classifyReviewEvent/classifyLanding wired into buildPipelineSpans
and the tool/turn endings in session.ts. A run-state failure now sits on its own
span beside a real PR check, so the queue still carries the PR's checks from GitHub.

Fixtures render a distinct label for every class; all 60 tests pass.

— hive: backend=pi model=lemonade/Ornith-1.5-35B-A3B-GGUF-Q6_K

🐝 Hive Agent: contributor | SHA: c1cb116

[castrojo]

Merged current main into this branch and resolved the two conflicts; both were keep-both, not either-or.

• state.ts — main added ItemCurrency/isItemTerminalBlocked at the same anchor where this branch adds classifyRunState. Both are kept. The one real decision: this branch reimplements runStateStatus as classStatus(classifyRunState(state)), which is the point of P1 — classify trace failures by PR, verification, environment, tool, and cancellation semantics #465 — the visual status derives from the reason, so the icon cannot drift from it. I kept that and dropped main's standalone switch, rather than leaving two implementations of the same function.
• tests/omp-review-mode.test.ts — import conflict; took the union (ciGlyph from this branch, parseMouseEvent from main).

No rebase, no --ours/--theirs, no force-push.

bash tests/omp-review-mode.sh          72/72
python3 tests/slay_state_contract.py   45/45
bash tests/bluefin-review.sh           OK
bash tests/test-registry.sh            OK

Over to CI.