docs: add third-party-tools.md links to guide index and observability

Add cross-references to newly created third-party-tools.md:
- guide/README.md: Add third-party-tools.md to contents table
- guide/observability.md: Add link to third-party-tools section

Related to RTK documentation integration (commit fdee330).

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

guide/README.md

@@ -8,6 +8,7 @@ Core documentation for mastering Claude Code.
 |------|-------------|------|
 | [ultimate-guide.md](./ultimate-guide.md) | Complete reference covering all Claude Code features | ~3 hours |
 | [mcp-servers-ecosystem.md](./mcp-servers-ecosystem.md) | **Community MCP servers**: 8 validated servers (Playwright, Semgrep, Kubernetes, etc.) with production configs | 25 min |
+| [third-party-tools.md](./third-party-tools.md) | **Community tools**: GUIs, TUIs, config managers, token trackers, alternative UIs | 15 min |
 | [claude-code-releases.md](./claude-code-releases.md) | Official release history (condensed) | 10 min |
 | [known-issues.md](./known-issues.md) | **Critical bugs tracker**: security issues, token consumption, verified community reports | 15 min |
 | [cheatsheet.md](./cheatsheet.md) | 1-page printable quick reference | 5 min |

guide/observability.md

@@ -410,5 +410,6 @@ find ~/.claude/logs -name "*.jsonl" -mtime +30 -delete
 - [Session Search Script](../examples/scripts/session-search.sh) - Fast session search & resume
 - [Session Logger Hook](../examples/hooks/bash/session-logger.sh)
 - [Stats Analysis Script](../examples/scripts/session-stats.sh)
+- [Third-Party Tools](./third-party-tools.md) - Community GUIs, TUIs, and dashboards (ccusage, ccburn, claude-code-viewer)
 - [Data Privacy Guide](./data-privacy.md) - What data leaves your machine
 - [Cost Optimization](./ultimate-guide.md#cost-optimization) - Tips to reduce spend