feat(cli): Add GitHub Actions annotations for CLI errors and warnings

[Swimburger]

Summary

Surface CLI errors and warnings as GitHub Actions annotations when running under GHA, so failures appear inline in the PR/run UI instead of being buried in the raw step log.

The screenshot motivating this: fern automations generate produced an "SDK generation failed (2/8 succeeded, 4 skipped)" summary table, but the GHA Annotations panel showed only the generic Process completed with exit code 1 — the user had to scroll the raw log to find which generator failed and why.

How it works

Two layers, both gated on GITHUB_ACTIONS=true:

1. Generic logger hook (in @fern-api/cli-logger) — every logger.error / logger.warn across the CLI also emits a ::error:: / ::warning:: workflow command on stdout. Covers fern check, fern generate, validation errors, etc. Status-only logs (omitOnTTY: true, e.g. the per-task "Failed." line) are filtered out so they don't burn through GitHub's per-step cap.

2. Structured per-generator annotations for fern automations generate — emitted from the GeneratorRunCollector after the run, anchored on the exact line in generators.yml (file=fern/apis/foo/generators.yml,line=42) so the annotation appears inline on the file in the PR's "Files changed" tab. Title format is <generator> failed (group=<group>, api=<api>) — explicit key=value qualifiers because generator names like fernapi/fern-python-sdk already contain /.

The structured emitter wraps its run in withSuppressedLoggerAnnotations(...) (a scoped runner with try/finally restoration) so per-generator failures don't get annotated twice — once with raw text from logger.error, once with the rich file= / line= metadata.

When the failure count exceeds GitHub's per-step cap (10), the structured emitter still emits one ::error:: per failure (GHA drops the overflow itself) and appends a trailing ::warning:: like "3 additional generator failures were hidden by GitHub's per-step annotation cap. See the step summary table for the full list." so reviewers know what's missing.

Related fix bundled in: auto-retry on 429 in automations mode

While verifying this PR with a real GHA run, every generator call hit 429 Too Many Requests from Fiddle. The CLI already has a --retry-rate-limited flag (bounded: 3 attempts, 2s→120s exponential backoff with jitter), but fern automations generate was passing false. Automation runs are unattended — failing the run and asking a human to re-trigger with a flag isn't useful — so this PR flips that default to true for automations only. fern generate (interactive) still requires the explicit flag. The retry warnings emitted during backoff are absorbed by withSuppressedLoggerAnnotations, so the panel stays clean and only the final post-retry failure (if any) becomes a ::error:: annotation.

Sanitization (per the GHA workflow command spec)

• ANSI escape codes (chalk colors) stripped from bodies and property values — they'd render as literal [31m...[39m noise in the panel.
• Embedded newlines in bodies encoded as %0A so multi-line errors stay one workflow command (GHA renders them as a multi-line annotation).
• Property values escape , : \r \n % per spec so they can't break out of the property list.

Out of scope

• fern check validation errors annotate via the generic logger hook with no file= / line= metadata. Anchoring those properly would need structured emission from a check-command emitter, not from logger.error — separate design pass.
• The 429s observed during empirical verification are independent of this PR's changes; the request/concurrency path is unchanged. Real fixes (client-side throttling on the createJob fan-out, or revisiting Fiddle's rate limit) are follow-ups.

Test plan

• pnpm turbo run test --filter @fern-api/cli-logger --filter @fern-api/cli — 33 + 637 tests pass
• pnpm check:fix clean
• End-to-end smoke test: simulated logger and structured annotation paths with GITHUB_ACTIONS=true and verified output matches expectations across env-var gate, suppression scope (incl. nested), level filter, omitOnTTY filter, prefix→title, and the cap-overflow warning
• Empirical verification on a real GHA run — published 5.9.0-rc.0, ran automations generate against a multi-workspace fern config, and confirmed: rich annotations rendered inline on generators.yml lines, %2C / %3A decoded correctly in titles, and no duplicate generic+structured annotations. Initial run also exposed the 429 issue, which motivated the retry default flip above.

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