docs(local): document DSN-less capture, client-side wiring, and -f ai filter

[sergical]

Summary

sentry local works well, but a few behaviors were undocumented and tripped up a user debugging logs/traces locally. This fills the gaps in the local command fragment + the agent guidance (which feeds the generated skill).

• No DSN required. With no DSN configured, events flow only to the local server — nothing reaches the user's Sentry org and no production quota is used. With a DSN set, the SDK sends to both. This is the main reassurance for using spotlight in local dev and wasn't stated.
• Client-side wiring caveat. sentry local run injects NEXT_PUBLIC_SENTRY_SPOTLIGHT, but no @sentry/* package reads it — only @sentry/node-core reads SENTRY_SPOTLIGHT (server-side). Browser/client SDKs need it referenced explicitly:

  Sentry.init({ spotlight: process.env.NEXT_PUBLIC_SENTRY_SPOTLIGHT ?? false });

  Other frameworks expose client env vars under different prefixes (Vite VITE_, CRA REACT_APP_). The docs previously implied the client var "just works."
• -f ai filter. Documented for watching gen_ai/mcp agent spans while iterating on an agent.

Where it lands

• docs/src/fragments/commands/local.md → the local docs page + generated skill reference.
• docs/src/content/docs/agent-guidance.md → a new "Capture Events Locally" workflow. Since the skill generator keeps code blocks but strips prose, the key facts are encoded as comments in a bash snippet so they reach the agent skill too.
• Regenerated SKILL.md + references/local.md accordingly (unrelated date-based reference drift left out; CI auto-commit handles that).

Notes

• Complements feat(local): add --verify, --timeout, auto-detect dev script, post-init verification #998 (which adds --verify/--timeout/dev-script auto-detect to local run). This PR only touches docs/guidance + the local reference, so the overlap is limited to the regenerated references/local.md.
• check:fragments and check:docs-sections pass locally.

🤖 Generated with Claude Code

[github-actions]

PR Preview Action v1.8.1
🚀 View preview at https://cli.sentry.dev/_preview/pr-1034/
Built to branch gh-pages at 2026-05-29 02:09 UTC. Preview will be ready when the GitHub Pages deployment is complete.

[github-actions]

Codecov Results 📊

✅ Patch coverage is 100.00%. Project has 4285 uncovered lines.
✅ Project coverage is 82%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    82.00%    82.00%        —%
==========================================
  Files          329       329         —
  Lines        23806     23806         —
  Branches     15543     15543         —
==========================================
+ Hits         19522     19521        -1
- Misses        4284      4285        +1
- Partials      1643      1642        -1

---

Generated by Codecov Action