fix(eve): ignore .devtools in eve dev watcher

[cfleissner-evisions]

Summary

Closes #1720.

AI SDK DevTools stores generation data in .devtools. That caused two problems in eve dev:

• The authored-source watcher treated writes as source changes and recompiled.
• Agent discovery treated .devtools/ as an unsupported directory and warned: Ignoring unsupported directory ".devtools/" in the agent root.

.eve is already a silent generated directory. This change treats .devtools the same way: ignore it in the watcher, classify it as an ignored agent-root directory (no warning), and skip it in source snapshots.

Validation

• pnpm --filter eve build
• pnpm --filter eve exec vitest run --config vitest.scenario.config.ts src/internal/nitro/host/dev-authored-source-watcher.scenario.test.ts -t "ignores generated directories" — 1 passed, 10 skipped
• pnpm --filter eve exec vitest run --config vitest.integration.config.ts src/discover/agent.integration.test.ts -t "silently ignores generated runtime directories" — 1 passed

Docs are not applicable.

Checklist

• I linked an issue with prior discussion confirming this change is wanted
• I ran the relevant checks from CONTRIBUTING.md
• I added tests and documentation where relevant
• I added a changeset if this touches the published eve package
• DCO sign-off passes for every commit (git commit --signoff)

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