fix(polyfill): add missing Bun.file().stat() shim for npm distribution

[BYK]

Summary

• Fixes CLI-1EA (14 events) and CLI-1EB (420 events, escalating) — both share a single root cause.
• Commit 9cb0d33 ("refactor(dsn): use Bun stat in regular-file guard", released in 0.29.0) swapped stat from node:fs/promises for Bun.file(path).stat() in isRegularFile(). The Node polyfill in script/node-polyfills.ts (injected at bundle time for the npm distribution) never implemented .stat(), so every DSN auto-detection call throws TypeError: Bun.file(...).stat is not a function on Node.
• The error is caught by isRegularFile's try/catch but then captured to Sentry (not in isIgnorableFileError's allow-list), so npm users on 0.29.0 silently lose .env DSN detection + .editorconfig project-root detection while spamming our Sentry project with handled TypeErrors.

Fix

Extend BunPolyfill.file(path) with stat: stat.bind(null, path) — aliases stat from node:fs/promises with the path pre-bound. No wrapper closure needed; matches Bun.file().stat()'s zero-arg signature exactly. fs.stat (not lstat) follows symlinks, matching Bun semantics — critical for detecting 1Password symlink → FIFO chains.

Minimal one-line addition to the polyfill + a new stat in the existing top-level node:fs/promises import.

Tests

• Extended test/script/node-polyfills.test.ts (the existing polyfillFile() reproduction) with 5 new .stat() cases: regular file, directory, non-existent path (ENOENT), symlink following, and parity with native Bun.file().stat().
• Added test/lib/node-polyfills-file-stat.test.ts — a mirror that lives under the bun run test:unit glob so CI actually runs it (the test/script/ directory is not in any CI test script per AGENTS.md).

All 39 polyfill tests pass; full bun test test/lib is green (4192 pass, 0 fail).

Release

Intended as the content of a 0.29.1 patch release (will cut after merge).

Verification

• bun run typecheck — clean
• bun run lint — only pre-existing warning in src/lib/formatters/markdown.ts (not touched)
• bun test test/lib — 4192 pass, 0 fail
• bun test test/script/node-polyfills.test.ts test/lib/node-polyfills-file-stat.test.ts — 39 pass

[github-actions]

Codecov Results 📊

✅ 138 passed | Total: 138 | Pass Rate: 100% | Execution Time: 0ms

📊 Comparison with Base Branch

Metric	Change
Total Tests	—
Passed Tests	—
Failed Tests	—
Skipped Tests	—

✨ No test changes detected

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 1942 uncovered lines.
❌ Project coverage is 95.3%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
- Coverage    95.32%    95.30%    -0.02%
==========================================
  Files          284       284         —
  Lines        41349     41348        -1
  Branches         0         0         —
==========================================
+ Hits         39415     39406        -9
- Misses        1934      1942        +8
- Partials         0         0         —

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