perf(server): unblock event loop on rate-limit waits and markitdown

Two complementary changes to mitigate intermittent TLS handshake
timeouts and "notifications/cancelled: Bad Request" seen against the
single-worker uvicorn deployment.

1. bedesten rate-limiter back-pressure
   - Add optional ``max_wait`` to ``_TokenBucket.acquire``: if the next
     wait would exceed it, raise ``BedestenRateLimited`` immediately
     instead of sleeping. After a server-side 429 the bucket pauses for
     up to 30s; previously a queued request sat in ``asyncio.sleep``
     for that whole window, holding the worker slot and pushing the
     MCP client past its cancellation timeout.
   - ``search_bedesten_unified`` / ``get_bedesten_document_markdown``
     catch ``BedestenRateLimited`` and reuse the existing structured
     429-style response, so callers get a fast, clean retry signal.
   - Tunable via ``BEDESTEN_RATE_MAX_WAIT_S`` (default 8.0s).

2. Offload sync markitdown conversions to a thread
   - Every ``markitdown.convert*`` call site is now wrapped in
     ``asyncio.to_thread(...)`` across 14 modules (bedesten, yargitay,
     danistay, anayasa norm + bireysel, uyusmazlik, emsal, rekabet,
     gib, kvkk, sayistay, bddk, sigorta_tahkim, kik_v2). PDF / large
     HTML parsing was stalling the event loop for seconds, which on a
     single-worker deployment delayed every other in-flight request
     and queued new TLS handshakes until they timed out.

Verified locally:
- ``ast.parse`` + ``importlib.import_module`` on all 15 modified files
- ``mcp_server_main.create_app()`` constructs successfully
- New ``_TokenBucket.acquire(max_wait=...)`` smoke-tested across 6
  paths: capacity-available, no-arg backward compat, max_wait raise,
  max_wait wait+succeed, ``penalize_until`` + max_wait fast-raise.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

sigorta_tahkim_mcp_module/client.py

@@ -1,5 +1,6 @@
 # sigorta_tahkim_mcp_module/client.py
 
+import asyncio
 import httpx
 from typing import Optional
 import logging
@@ -202,7 +203,11 @@ class SigortaTahkimApiClient:
         response.raise_for_status()
 
         pdf_stream = io.BytesIO(response.content)
-        result = self.markitdown.convert_stream(pdf_stream, file_extension=".pdf")
+        # markitdown is sync; offload to thread so PDF parsing doesn't block
+        # the event-loop / other in-flight MCP requests.
+        result = await asyncio.to_thread(
+            self.markitdown.convert_stream, pdf_stream, file_extension=".pdf"
+        )
         return result.text_content.strip(), pdf_url
 
     def _split_into_decisions(self, markdown_content: str) -> list[tuple[str, str]]: