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/config.py

@@ -38,6 +38,7 @@ DEFAULT_FETCH_TIMEOUT_SECONDS = 300.0
 DEFAULT_FETCH_MAX_BYTES = 8_000_000
 DEFAULT_RSEARCH_URL = "https://rsearch.app.molodetz.nl"
 DEFAULT_RSEARCH_TIMEOUT_SECONDS = 300.0
+DEFAULT_EMAIL_TIMEOUT_SECONDS = 30.0
 
 
 @dataclass(frozen=True)
@@ -72,6 +73,8 @@ class Settings:
     rsearch_enabled: bool
     rsearch_url: str
     rsearch_timeout_seconds: float
+    email_enabled: bool
+    email_timeout_seconds: float
     daily_limit_usd: float
 
 
@@ -152,6 +155,11 @@ def load_settings() -> Settings:
         rsearch_timeout_seconds=float(
             os.environ.get("DEVII_RSEARCH_TIMEOUT", DEFAULT_RSEARCH_TIMEOUT_SECONDS)
         ),
+        email_enabled=os.environ.get("DEVII_EMAIL_ENABLED", "1").lower()
+        in ("1", "true", "yes", "on"),
+        email_timeout_seconds=float(
+            os.environ.get("DEVII_EMAIL_TIMEOUT", DEFAULT_EMAIL_TIMEOUT_SECONDS)
+        ),
         daily_limit_usd=0.0,
     )
 
@@ -176,6 +184,8 @@ FIELD_FETCH_TIMEOUT = "devii_fetch_timeout"
 FIELD_RSEARCH_ENABLED = "devii_rsearch_enabled"
 FIELD_RSEARCH_URL = "devii_rsearch_url"
 FIELD_RSEARCH_TIMEOUT = "devii_rsearch_timeout"
+FIELD_EMAIL_ENABLED = "devii_email_enabled"
+FIELD_EMAIL_TIMEOUT = "devii_email_timeout"
 
 LESSONS_DB_PATH = os.environ.get("DEVII_LESSONS_DB", str(DEVII_LESSONS_DB))
 
@@ -234,5 +244,9 @@ def build_settings(
         rsearch_timeout_seconds=float(
             config.get(FIELD_RSEARCH_TIMEOUT) or DEFAULT_RSEARCH_TIMEOUT_SECONDS
         ),
+        email_enabled=bool(config.get(FIELD_EMAIL_ENABLED, True)),
+        email_timeout_seconds=float(
+            config.get(FIELD_EMAIL_TIMEOUT) or DEFAULT_EMAIL_TIMEOUT_SECONDS
+        ),
         daily_limit_usd=effective_daily_limit(config, owner_kind, is_admin),
     )