[docs] Add observe() quickstart page to docs.tealtiger.ai

[nagasatish007]

Summary

The docs site needs a proper quickstart guide for the observe() feature shipped in v1.4.

What to do

• Edit or create TealTiger-Docs/concepts/observe-mode.mdx
• Show TypeScript + Python examples side by side
• Explain: what observe() does, what getCost() returns, what freeze() does
• Add the progressive disclosure table (Level 0-3)
• Keep it under 200 lines

Page structure

1. One-liner — what observe() is (1 sentence)
2. Install — npm/pip commands
3. TypeScript example — 5 lines
4. Python example — 5 lines
5. What you get automatically — bullet list of capabilities
6. getCost() response shape — show the ObserveCostSummary fields
7. freeze() / unfreeze() — kill switch usage
8. Supported providers — list of 12
9. Performance — under 5ms, in-process, offline-capable
10. Next steps — link to guardrails, policies, dashboard

Acceptance criteria

• Page renders correctly on docs.tealtiger.ai (Mintlify MDX format)
• TypeScript and Python examples are both present
• No broken links
• Added to navigation in docs.json if not already present

Helpful links

• Docs repo: https://github.com/agentguard-ai/TealTiger-Docs
• Existing nav: check docs.json for the "Core Concepts" section
• Source reference: packages/tealtiger-sdk/src/observe/