When the user sets template="hermes", surface a provider dropdown
(15 providers, defaulting to anthropic) and a masked API key input.
On submit the chosen key is sent as `secrets: { [ENV_VAR]: key }` so
the backend can persist it encrypted before the container boots,
fixing the silent preflight failure reported in #493.
- Adds HERMES_PROVIDERS constant (exported for tests)
- Validates API key presence before POST when template is hermes
- Uses violet accent to visually distinguish the hermes section
- 11 new unit tests covering picker visibility, default, env-var
mapping, validation, and POST payload shape
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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