feat(reliability): add provider skip-error rules and retry policy

[nguyenha935]

Summary

• Supersedes fix: handle Antigravity capacity and stream usage #2370 while preserving its Antigravity capacity fallback, stream usage, and Recent Requests fixes.
• Adds request-scoped transport retry policy and configurable provider skip-error rules.
• Adds a compact Settings UI, strict API validation, and an idempotent migration for the legacy Antigravity capacity behavior.

Behavior

• maxTransportAttempts caps in-place transport attempts per request without mutating cached executor config.
• providerSkipRules supports kind, status, and contains conditions with AND semantics and first-match ordering.
• Rules can retry the current transport or skip to the next account/model; headerTimeoutMs customizes connect/header timeout and sweep opts a skip rule into a full account-pool resweep.
• Connect timeout classification uses an attempt-local closure flag, so caller aborts, network failures, and real HTTP errors remain distinct.
• Combo fail-fast metadata is kept in an in-process WeakMap; it is never serialized into response headers or bodies.
• Transport retry policy does not change Codex SSE-overload retry, namespace compatibility retry, token refresh, or other higher-level retry loops.

Migration and UI

• Schema migration v2 seeds the former Antigravity 503 + capacity behavior as an editable skip + sweep rule when it is not already covered, while respecting existing user rules.
• Settings validation limits attempts to 1..5, rules to 100, and validates match/action/timeout/sweep combinations before writing.
• The responsive Skip-error rules modal uses compact, clearly separated fields in light and dark themes and merges static providers with dynamic compatible provider nodes.

Test plan

• 41 targeted skip-rule, fail-fast, routing metadata, no-auth, concurrency, modal, and Antigravity capacity tests passed with --unhandled-rejections=warn.
• 32 inherited Antigravity Recent Requests, retry-hook, request-detail usage, migration-chain, and seed tests passed.
• git diff --check passed.
• npm run build passed.

Notes

• No production patch, database, screenshot helper, or generated snapshot is included in this PR.