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/openai_gateway/gateway.py

@@ -225,6 +225,7 @@ class GatewayRuntime:
         handle_start = time.monotonic()
         messages = body.get("messages", []) or []
 
+        vision_cost = 0.0
         if cfg["gateway_vision_enabled"]:
             augmenter = VisionAugmenter(
                 cfg["gateway_vision_url"],
@@ -238,6 +239,7 @@ class GatewayRuntime:
             )
             messages = await augmenter.augment_messages(client, messages)
             self.vision_calls += augmenter.calls
+            vision_cost = augmenter.cost_usd
 
         messages = apply_system_directives(messages, cfg.get("gateway_system_preamble", ""))
 
@@ -300,9 +302,13 @@ class GatewayRuntime:
             base["success"] = success
             base["error_category"] = category
             base["usage"] = usage
-            return usage_response_headers(
-                self._ledger.record(base, pricing, context_map)
-            )
+            row = self._ledger.record(base, pricing, context_map)
+            headers = usage_response_headers(row)
+            if vision_cost and headers:
+                chat_cost = float((row or {}).get("cost_usd") or 0.0)
+                headers["X-Gateway-Cost-USD"] = f"{chat_cost + vision_cost:.8f}"
+                headers["X-Gateway-Vision-Cost-USD"] = f"{vision_cost:.8f}"
+            return headers
 
         if timing["circuit_open"]:
             resp_headers = finalize(503, False, "circuit_open")
@@ -370,6 +376,7 @@ class GatewayRuntime:
         self, body: dict, cfg: dict, owner: tuple, user_agent: str, log=None
     ):
         log = log or (lambda message: None)
+        vision_cost = 0.0
         overlay = embed_overlay(body.get("model"), cfg)
         if overlay:
             cfg = {**cfg, **overlay}
@@ -465,9 +472,13 @@ class GatewayRuntime:
             base["success"] = success
             base["error_category"] = category
             base["usage"] = usage
-            return usage_response_headers(
-                self._ledger.record(base, pricing, context_map)
-            )
+            row = self._ledger.record(base, pricing, context_map)
+            headers = usage_response_headers(row)
+            if vision_cost and headers:
+                chat_cost = float((row or {}).get("cost_usd") or 0.0)
+                headers["X-Gateway-Cost-USD"] = f"{chat_cost + vision_cost:.8f}"
+                headers["X-Gateway-Vision-Cost-USD"] = f"{vision_cost:.8f}"
+            return headers
 
         if timing["circuit_open"]:
             resp_headers = finalize(503, False, "circuit_open")
@@ -538,6 +549,7 @@ class GatewayRuntime:
         log=None,
     ):
         log = log or (lambda message: None)
+        vision_cost = 0.0
         client, sem = self._ensure(cfg)
         pricing = pricing_from_cfg(cfg)
         context_map = parse_context_map(cfg.get("gateway_model_context_map"))
@@ -583,9 +595,13 @@ class GatewayRuntime:
             base["success"] = success
             base["error_category"] = category
             base["usage"] = usage
-            return usage_response_headers(
-                self._ledger.record(base, pricing, context_map)
-            )
+            row = self._ledger.record(base, pricing, context_map)
+            headers = usage_response_headers(row)
+            if vision_cost and headers:
+                chat_cost = float((row or {}).get("cost_usd") or 0.0)
+                headers["X-Gateway-Cost-USD"] = f"{chat_cost + vision_cost:.8f}"
+                headers["X-Gateway-Vision-Cost-USD"] = f"{vision_cost:.8f}"
+            return headers
 
         if timing["circuit_open"]:
             resp_headers = finalize(503, False, "circuit_open")