restructure docs: split triggers into usage pages, add model resolution docs

- split triggers.mdx into direct-prompting, pr-reviews, issue-enrichment, coding-tasks
- rename manual-setup.mdx to headless-action.mdx (CI integration)
- reorganize sidebar into Getting started / Usage / Reference groups
- add redirects for /triggers and /manual-setup
- add PULLFROG_MODEL env var support across action, workflows, and docs
- rewrite models.mdx with aliases, free models, resolution chain, routers
- update all cross-references in app, components, and docs

Made-with: Cursor

utils/docker.ts

@@ -117,6 +117,7 @@ const testEnvAllowList = new Set([
   "ANTHROPIC_API_KEY",
   "GEMINI_API_KEY",
   "GOOGLE_GENERATIVE_AI_API_KEY",
+  "PULLFROG_MODEL",
   "OPENCODE_MODEL",
   "LOG_LEVEL",
   "DEBUG",