docs: document server-side rendering pipeline, response timing middleware, and Telegram pairing API

- Add comprehensive documentation for backend content rendering in AGENTS.md, detailing the new `render_content` and `render_title` Jinja globals built on mistune with media processing, emoji shortcodes, and XSS protection
- Document the `X-Response-Time` header and bottom-left render time indicator in README.md
- Update bot token pricing documentation to clarify fallback vs gateway cost headers
- Add `email_accounts` to soft-delete tables and `idx_users_role` composite index in database schema
- Implement `telegram_pairings` and `telegram_links` table creation with column migration and indexes
- Add `/profile/{username}/telegram` endpoint to docs API with request/unpair actions
- Register `TelegramService` in main.py lifespan and add `response_timing` middleware emitting `X-Response-Time` header
- Introduce `TelegramPairForm` model and `guard_public_host_sync` synchronous host validation function

devplacepy/services/devii/llm.py

@@ -9,7 +9,7 @@ import httpx
 
 from devplacepy import stealth
 from .config import Settings
-from .cost import record_usage
+from .cost import record_cost, record_usage
 from .errors import LLMError
 
 logger = logging.getLogger("devii.llm")
@@ -67,6 +67,7 @@ class LLMClient:
             raise LLMError("Model response contained no message.", body=str(data)[:500])
 
         record_usage(data.get("usage"))
+        self._record_native_cost(response)
         logger.debug(
             "LLM response received (tool_calls=%s)", bool(message.get("tool_calls"))
         )
@@ -94,6 +95,7 @@ class LLMClient:
         except (ValueError, KeyError, IndexError) as exc:
             raise LLMError("Model endpoint returned an unexpected response.") from exc
         record_usage(data.get("usage"))
+        self._record_native_cost(response)
         return content
 
     async def summarize(self, text: str) -> str:
@@ -124,8 +126,19 @@ class LLMClient:
                 "Model summarization returned an unexpected response."
             ) from exc
         record_usage(data.get("usage"))
+        self._record_native_cost(response)
         return content
 
+    @staticmethod
+    def _record_native_cost(response: httpx.Response) -> None:
+        raw = response.headers.get("X-Gateway-Cost-USD")
+        if raw is None:
+            return
+        try:
+            record_cost(float(raw))
+        except (TypeError, ValueError):
+            return
+
     @staticmethod
     def _reason(response: httpx.Response) -> str:
         try: