fix(config): handle 'local-agent' provider in getLLMConfig (#118)

* fix(config): handle 'local-agent' provider in getLLMConfig

Routing a mission through a connected local CLI agent (Claude Code / Codex /
Hermes) sets the provider to `local-agent`, but getLLMConfig's switch had no
case for it, so it fell through to `default` and threw
`Unknown provider: local-agent`. This aborted every keyless mission with a
REFUSED, even though `local-agent` is a registered provider wired to
LocalAgentAdapter everywhere else.

Add a `case 'local-agent'` mirroring `codex`: keyless (no apiKey/baseUrl), with
the connected agent id (codex|claude|hermes) carried in `model` and a sensible
default. Verified getLLMConfig('local-agent','claude') now resolves to
{provider:'local-agent', model:'claude'} instead of throwing.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* test(config): regression coverage for local-agent provider (#118)

Addresses review feedback: the fix had no test, so removing the
`case 'local-agent'` would leave CI green while re-breaking keyless missions.

Adds focused assertions in src/__tests__/local-agent-provider.test.ts:
- local-agent + model `claude` resolves to provider/model with no apiKey/baseUrl
- any supported agent id (codex|claude|hermes) passed as model is preserved
- omitting the model falls back to the default agent id
- getLLMConfig('local-agent') no longer throws
- AVAILABLE_MODELS['local-agent'] surfaces the connected-agent ids

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: hoptoad-off <mvzmysun@gmail.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>