Load .env automatically at startup so the API key doesn't depend on the launch shell

[Hrt-Htk]

Summary

The proxies read the API key from the process environment only
(os.environ.get("LLAMA_API_KEY")), but nothing loads .env. So whether
the server comes up authenticated depends entirely on the shell that launched it
having $env:LLAMA_API_KEY exported.

Observed:

• .env contains LLAMA_API_KEY, but no code reads it (stdlib + aiohttp only, no
  python-dotenv).
• No PowerShell profile sets it (none exist), and it is not a persistent
  env var (User/Machine scope both empty).
• watchdog.ps1 / watchdog-embed.ps1 don't load .env either.

Result: launching from a fresh terminal (or a Task Scheduler context) that didn't
export the key brings the proxy up with auth disabled (the auth_middleware
skips auth when config.api_key is falsy), which is a silent security footgun.

Proposed fix

Load .env at startup in both proxy.py and embed_proxy.py using stdlib only
(no new dependency): parse KEY=VALUE lines from .env next to the script and
os.environ.setdefault(...) each one.

• Use setdefault so an already-exported env var always wins (no surprise
  overrides; explicit env still takes precedence).
• Tolerate a missing .env (no-op), comments (#), blank lines, and quoted
  values.
• Keep it shared (e.g. a small helper) so both proxies behave identically.

Acceptance criteria

• Launching either proxy from a shell with no LLAMA_API_KEY exported still
  comes up authenticated using the value in .env.
• An explicitly exported LLAMA_API_KEY overrides the .env value.
• Missing .env does not crash startup.
• No new third-party dependencies; .env stays gitignored.