feat(telegram): add dedicated TELEGRAM_PROXY env var and config.yaml proxy_url support

Pass platform_env_var="TELEGRAM_PROXY" to resolve_proxy_url() in both
telegram.py (main connect) and telegram_network.py (fallback transport),
so a Telegram-specific proxy takes priority over the generic HTTPS_PROXY.

Also bridge telegram.proxy_url from config.yaml to the TELEGRAM_PROXY
env var (env var takes precedence if both are set), add OPTIONAL_ENV_VARS
entry, docs, and tests.

Composite salvage of four community PRs:
- Core approach (both call sites): #9414 by @leeyang1990
- config.yaml bridging + docs: #6530 by @WhiteWorld
- Naming convention: #9074 by @brantzh6
- Earlier proxy work: #7786 by @ten-ltw

Closes #9414, closes #9074, closes #7786, closes #6530

Co-authored-by: WhiteWorld <WhiteWorld@users.noreply.github.com>
Co-authored-by: brantzh6 <brantzh6@users.noreply.github.com>
Co-authored-by: ten-ltw <ten-ltw@users.noreply.github.com>

hermes_cli/config.py

@@ -1252,6 +1252,12 @@ OPTIONAL_ENV_VARS = {
         "password": False,
         "category": "messaging",
     },
+    "TELEGRAM_PROXY": {
+        "description": "Proxy URL for Telegram connections (overrides HTTPS_PROXY). Supports http://, https://, socks5://",
+        "prompt": "Telegram proxy URL (optional)",
+        "password": False,
+        "category": "messaging",
+    },
     "DISCORD_BOT_TOKEN": {
         "description": "Discord bot token from Developer Portal",
         "prompt": "Discord bot token",