feat(combo): add Guarded Priority routing

[xz-dev]

Summary

Adds Guarded Priority, a dedicated Combo routing strategy for cost-safe ordered fallback.

• Always dispatches the highest-priority eligible child.
• Returns non-matching failures unchanged; transient disconnects, timeouts, plain 429/408/502 and other failures cannot spill into later paid nodes.
• Only a matching Hard Offline condition may cool the selected account/node and advance.
• Supports explicit quota/account-unavailable signals, authoritative HTTP 503, and bounded Safe JSON Logic.
• Defaults Hard Offline cooldown to five minutes while preserving explicit persisted values.
• Keeps nested paid pools opaque through nestedComboMode: execute and rejects flattening, hedging, shadow routing, pin/reordering bypasses.
• Adds a dedicated Dashboard configuration stage; ordinary Priority remains unchanged.

Closes #9677.

Verification

• 44 focused runtime/schema/draft/request-path tests pass.
• 2 Dashboard component tests pass.
• Actual chat-route tests cover dynamic unpinned A/B pools, no-spill non-matches, matching 503 advancement, global fallback suppression, pre-dispatch unavailability, and ordinary Priority controls.
• Mutation checks prove account-level and global-fallback guards are load-bearing.
• Portable test harness passes from a second absolute checkout path.
• combos/page.tsx remains within its frozen file-size baseline (4646/4647).
• Prettier, scoped ESLint, locale parsing, tracked-artifact and diff checks pass.

Known release-base drift

Repository-wide gates still report unrelated existing release/v3.8.50 issues (including the missing antigravityProjectPersistence.ts, duplicate migration 134, unrelated frozen file-size drift, and existing docs/quality failures). No baseline was weakened or rebased in this PR.

[xz-dev]

Guarded Priority follow-up deployed from the complete production patch stack.

Deployment receipt:

• Approved PR head: d63b6dea911dcc0a150a814cbf25561a9466aea9 (single compact commit)
• Production integration: 25f375485ff61e2d49a6047451b2540a77c0d96d over production parent 329fe20fb61a4b0d909bcdac4046ecd6bcebccde
• GitHub Actions: https://github.com/xz-dev/OmniRoute/actions/runs/31175444003
• GHCR digest: sha256:e877112d01dbde791c8fbced0101fde4fe7bda15183c92a242386a0a0c2eab87
• Isolated blank-data smoke: passed
• Isolated production-environment + consistent SQLite snapshot smoke: passed, including encrypted-credential bootstrap
• Production health: healthy, HTTP 200, SQLite integrity_check=ok
• gpt-5.6-{sol,terra,luna} migrated atomically to guarded-priority, five-minute cooldown, nested paid-cache fallback preserved in execute mode

Focused acceptance evidence remains 44/44 runtime/schema/request-path tests plus 2/2 Dashboard component tests. Actual route tests cover dynamic unpinned account pools, nonmatching no-spill responses, matching 503 advancement, global fallback suppression, and ordinary Priority controls.

The remaining upstream PR check failures are release-base drift already documented in the PR (missing antigravityProjectPersistence.ts, duplicate migration 134, unrelated docs/quality/file-size/lint issues). Semgrep and change classification pass; the fork image build succeeds from the full production integration.

[diegosouzapw]

The release/v3.8.50 base now includes base-red fixes (typecheck tabs fix #9729, ESLint suppression prune + combo test alignment #9774). Your branch's CI still shows the old failures because it's based on the pre-fix base. Please merge/rebase the latest release/v3.8.50 into your branch to pick up the fixes — the conflict in comboStructure.ts is resolved on this side if you want to take it.