Implement startup-no-evidence evidence bundle + classifier (US-001)

Adds typed worker.startup_no_evidence event with evidence bundle when worker
startup times out. The classifier attempts to down-rank the vague bucket into
specific failure classifications:
- trust_required
- prompt_misdelivery
- prompt_acceptance_timeout
- transport_dead
- worker_crashed
- unknown

Evidence bundle includes:
- Last known worker lifecycle state
- Pane/command being executed
- Prompt-send timestamp
- Prompt-acceptance state
- Trust-prompt detection result
- Transport health summary
- MCP health summary
- Elapsed seconds since worker creation

Includes 6 regression tests covering:
- Evidence bundle serialization
- Transport dead classification
- Trust required classification
- Prompt acceptance timeout
- Worker crashed detection
- Unknown fallback

Closes Phase 1.6 from ROADMAP.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

rust/crates/runtime/src/recovery_recipes.rs

@@ -48,7 +48,9 @@ impl FailureScenario {
             WorkerFailureKind::TrustGate => Self::TrustPromptUnresolved,
             WorkerFailureKind::PromptDelivery => Self::PromptMisdelivery,
             WorkerFailureKind::Protocol => Self::McpHandshakeFailure,
-            WorkerFailureKind::Provider => Self::ProviderFailure,
+            WorkerFailureKind::Provider | WorkerFailureKind::StartupNoEvidence => {
+                Self::ProviderFailure
+            }
         }
     }
 }