feat(http): use httpx with pooled connections and browser headers

Add httpx and route Bilibili and Telegram requests through pooled clients with keepalive and explicit timeouts. Align Bilibili headers with data/raw-request.txt: Chrome 155 UA, sec-ch-ua, space.bilibili.com origin, folder-specific referer, and priority header. Close replaced clients when credentials change. Add transport contract tests and live read-only validation for nav, folder sync, WBI search, and Telegram getUpdates.

pyproject.toml

@@ -10,7 +10,9 @@ readme = "README.md"
 requires-python = ">=3.14,<3.15"
 license = { text = "MIT" }
 authors = [{ name = "bili-fav contributors" }]
-dependencies = []
+dependencies = [
+    "httpx>=0.28.1",
+]
 
 [project.scripts]
 bili-fav = "favsort:main"