docs(integrations): add Pydantic AI tracing page

[SuhaniNagpal7]

Summary

• Adds a new TraceAI integration page for Pydantic AI at /docs/integrations/traceai/pydantic_ai, following the 5-section sibling template (Install → Env vars → register → instrument → run).
• Wires the page into both sidebars (Tracing → Frameworks & Agents, Integrations → Frameworks & Agents) and both overview grids (/docs/tracing/auto, /docs/integrations). Both nav entries point at the same file, matching the n8n precedent in navigation.ts.
• Uses env-var auth (FI_API_KEY/FI_SECRET_KEY) rather than the register(api_key=...) form shown in the upstream traceAI repo example, because fi_instrumentation.register() does not accept an api_key kwarg and that call would raise TypeError at runtime.

What changed

File	Change
src/pages/docs/integrations/traceai/pydantic_ai.mdx	New page (title, description, 5 sections, @agent.tool example)
src/lib/navigation.ts	+1 entry in each of the Tracing and Integrations sidebars, both pointing at the new page
src/pages/docs/integrations/index.mdx	+1 Pydantic AI card in the TraceAI grid
src/pages/docs/tracing/auto/index.mdx	+1 Pydantic AI card in the auto-instrumentation grid

Verification

• astro dev compiled the new MDX with zero errors / zero browser console errors. Page returns 200, titles + H2s + code blocks + sidebar entry + prev/next nav all render.
• Live runtime smoke test against api.futureagi.com: ran the literal Step 2-5 code from the page using FI_API_KEY/FI_SECRET_KEY + OPENAI_API_KEY. The register() call succeeded, PydanticAIInstrumentor instrumented, agent.run_sync(...) returned the expected tool-backed answer, and the trace landed in the PYDANTIC_AI_APP project (1 trace, status OK, gpt-4o / openai / 181 tokens / $0.0007 captured with full gen_ai.* + llm.* attributes).
• Both overview grids and both sidebars confirmed via curl to expose the new card / nav entry.

Test plan

• astro dev and confirm /docs/integrations/traceai/pydantic_ai renders with the 5 sections.
• Confirm the Pydantic AI entry shows up in both the Tracing and Integrations sidebars (under "Frameworks & Agents", between Smol Agents and Instructor).
• Confirm the Pydantic AI card appears on both /docs/tracing/auto and /docs/integrations overview grids.
• Optional: copy-paste the Step 2-5 code with real keys and confirm a trace shows up in your FAGI workspace.