fix(review): exit non-zero when a partial run has real item failures

[HoneyTyagii]

Summary

Fixes #1027.

ocr review exits 0 on a partial run (some items completed, some failed with timeout/provider errors), so CI cannot detect an incomplete review or a misconfigured harness from the exit status alone. The GitHub Action then skips posting (Post review comments gates on OCR_EXIT_CODE == '0') while the job stays green.

Change

• reviewResultError (cmd/opencodereview/review_cmd.go): a partial manifest whose failed set contains any non-budget item now returns an error, so the run exits non-zero. Budget-only partials (the documented --max-tokens-budget controlled-truncation contract) keep exiting 0. Partial results are still published before the non-zero exit, so JSON consumers keep the full coverage diagnosis.
• Updated the unit and e2e tests that pinned the old exit-0 contract, including a new mixed budget+provider partial case that counts only real failures.
• Docs synced: --max-tokens-budget flag help, action.yml input description, and the exit-codes tables / FAQ entries across en/zh/ja/ko/ru pages.

Verification

• go build ./..., go vet ./cmd/..., gofmt -s -l clean
• go test ./cmd/... ./internal/session/... passes (LC_ALL=C)
• New pinned cases: partial with a timeout failure exits non-zero; budget-only partial still exits 0

Fixes #1027

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[CLAassistant]

All committers have signed the CLA.

[github-actions]

✅ OpenCodeReview: Review complete: 0 finding(s) across 3 selected item(s).

[rajpratham1]

The new exit-code behavior is directionally correct, but the process status now depends on nonBudgetFailures() treating every non-FailureBudget classification as a real failure. Since this changes the CLI/CI contract, please add coverage for the other possible failure classifications and verify that only controlled budget truncation returns 0 for a partial run. After those cases are covered, this should be ready to merge.