Improve OpenCode ACP startup timeout guidance

[baron]

Summary

• Add a typed ACPRequestTimeoutError so provider normalization can recognize ACP request timeouts without string matching.
• Capture ACP agentInfo from initialize and include it in timeout diagnostics, so OpenCode startup failures can show a version/agent indicator.
• Normalize OpenCode startup-phase ACP timeouts (initialize, authenticate, session/new, session/load) into actionable upgrade/verification guidance while preserving the original timeout detail.
• Ensure Settings/model-discovery OpenCode ACP failures use the same provider normalization path.

Minimization pass

• Reviewed with Claude Fable 5 High in the task worktree.
• Removed the low-value passthrough test that only covered pre-existing fallback behavior.
• Kept two cheap provider-normalization tests: startup timeout guidance and prompt-timeout no-leak boundary.
• Kept the single new diagnostic line because it goes through existing ACP diagnostics and records exactly the OpenCode version datum needed for support.

Conflict resolution

• Merged current origin/main (v1.0.24) into the PR branch without force-pushing.
• Resolved the only conflict in Scripts/Fixtures/test-suite-contract-ledger.tsv by taking main's reconciled ledger and reinserting the two OpenCode test rows under the updated schema (execution_tier=routine).
• GitHub now reports the branch as mergeable; remaining PR blocking is queued/in-progress CI.

Validation

• make dev-format ✅
• make dev-test FILTER=OpenCodeACPLaunchResolverTests ✅ — 12 tests, 0 failures
• make dev-test-list ✅
• python3 Scripts/test_suite_optimizer.py verify-ledger --ledger Scripts/Fixtures/test-suite-contract-ledger.tsv ✅ — 2916 ledger rows validated
• make dev-lint ✅ — 0 violations
• make dev-swift-build PRODUCT=RepoPrompt ✅
• make dev-smoke ✅
• .agents/skills/rpce-contribution-check/scripts/preflight.sh commit ✅
• .agents/skills/rpce-contribution-check/scripts/preflight.sh push ✅

Related to #117.