docs: document notification-routing skill

[diberry]

Closes #67

Documents the notification-routing skill (pub-sub channel routing to prevent alert fatigue).

Source: bradygaster#625 by Tamir Dresher (commit \�9c06b09)

Working as PAO (DevRel)

Changes

• New docs page: \eatures/notification-routing.md\ — channel config schema, CHANNEL: tag convention, routing dispatcher, anti-patterns, distributed systems context
• Navigation entry added in
  avigation.ts\ (Features section, before Notifications)
• Test assertion updated in \docs-build.test.ts\ (\EXPECTED_FEATURES\ array)

Quality checks

• Microsoft Style Guide: sentence-case headings, active voice, second person, present tense
• Scannability: tables for config and anti-patterns, bullets for symptoms, code blocks for examples
• Deep linking: cross-references to Notifications, Skills, and Distributed Mesh pages
• Single commit, docs-test sync

⚠️ Awaiting Flight + FIDO review before merge.

[diberry]

Closing — pushed to wrong branch. Reopening from correct branch.