feat(adapters): external adapter plugin system with dynamic UI parser

- Plugin loader: install/reload/remove/reinstall external adapters
  from npm packages or local directories
- Plugin store persisted at ~/.paperclip/adapter-plugins.json
- Self-healing UI parser resolution with version caching
- UI: Adapter Manager page, dynamic loader, display registry
  with humanized names for unknown adapter types
- Dev watch: exclude adapter-plugins dir from tsx watcher
  to prevent mid-request server restarts during reinstall
- All consumer fallbacks use getAdapterLabel() for consistent display
- AdapterTypeDropdown uses controlled open state for proper close behavior
- Remove hermes-local from built-in UI (externalized to plugin)
- Add docs for external adapters and UI parser contract

adapter-plugin.md

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+- Created branch: feat/external-adapter-phase1
+
+   I started phase 1 in the most merge-friendly way I could: small central changes, reusing existing registry patterns instead of inventing a whole new plugin system up front.
+
+   What I changed
+
+   1. Server adapter registry is now mutable
+   Files:
+  - server/src/adapters/registry.ts
+  - server/src/adapters/index.ts
+
+   Added:
+  - registerServerAdapter(adapter)
+  - unregisterServerAdapter(type)
+  - requireServerAdapter(type)
+
+   Kept the existing built-in registry shape, but changed initialization so built-ins are registered into a mutable map on startup.
+
+   Why this is merge-friendly:
+  - existing built-in adapter definitions stay where they already are
+  - existing lookup helpers still exist
+  - no big architectural rewrite yet
+
+   1. Runtime adapter validation moved to server routes
+   File:
+  - server/src/routes/agents.ts
+
+   Added:
+  - assertKnownAdapterType(...)
+
+   Used it in:
+  - /companies/:companyId/adapters/:type/models
+  - /companies/:companyId/adapters/:type/detect-model
+  - /companies/:companyId/adapters/:type/test-environment
+  - POST /companies/:companyId/agents
+  - POST /companies/:companyId/agent-hires
+  - PATCH /agents/:id when adapterType is touched
+
+   Why:
+  - shared schemas can now allow external adapter strings
+  - server becomes the real source of truth for “is this adapter actually registered?”
+
+   1. Shared adapterType validation is now open-ended for inputs
+   Files:
+  - packages/shared/src/adapter-type.ts
+  - packages/shared/src/validators/agent.ts
+  - packages/shared/src/validators/access.ts
+  - packages/shared/src/index.ts
+
+   Changed input validation from hardcoded z.enum(AGENT_ADAPTER_TYPES) to:
+  - agentAdapterTypeSchema
+  - optionalAgentAdapterTypeSchema
+
+   These accept any non-empty string.
+
+   Important:
+  - I did not remove AGENT_ADAPTER_TYPES from constants
+  - I did not change the built-in type unions yet
+  - this keeps the change minimal and limits blast radius
+
+   So:
+  - input payloads can carry external adapter types
+  - actual acceptance still depends on server registry validation
+
+   1. UI adapter registry is now mutable too
+   Files:
+  - ui/src/adapters/registry.ts
+  - ui/src/adapters/index.ts
+
+   Added:
+  - registerUIAdapter(adapter)
+  - unregisterUIAdapter(type)
+  - findUIAdapter(type)
+
+   Built-ins are still registered from the same file, same pattern as server.
+
+   1. Began switching UI adapter lists toward the registry
+   Files:
+  - ui/src/adapters/metadata.ts
+  - ui/src/components/AgentConfigForm.tsx
+  - ui/src/pages/NewAgent.tsx
+
+   Changed:
+  - AgentConfigForm adapter list now comes from registered UI adapters via metadata helper
+  - NewAgent supported adapter set now derives from listUIAdapters()
+
+   Why:
+  - phase 1 should start reducing hardcoded UI lists
+  - but without rewriting every page at once
+
+   1. Tests added first, then implementation
+   New tests:
+  - server/src/__tests__/adapter-registry.test.ts
+  - server/src/__tests__/agent-adapter-validation-routes.test.ts
+  - ui/src/adapters/registry.test.ts
+  - packages/shared/src/adapter-types.test.ts
+
+   Small test mock fix:
+  - server/src/__tests__/agent-skills-routes.test.ts
+
+   Current status
+
+   The branch is created and the phase-1 code is started.
+
+   I also followed TDD in spirit:
+  - wrote failing tests first for missing register/unregister APIs
+  - then implemented the registry changes
+
+   What is not finished yet
+
+   I have not finished the green/stabilization pass yet.
+
+   I still need to:
+  - run the targeted tests again after the implementation changes
+  - fix any TS / mocking fallout
+  - decide how far to take phase-1 UI wiring in this branch before stopping
+
+   Also, I intentionally did not yet touch the bigger hardcoded surfaces like:
+  - NewAgentDialog
+  - OnboardingWizard
+  - InviteLanding
+  - duplicated adapterLabels maps
+  - plugin manifest / plugin loader adapter contributions
+
+   That is deliberate.
+   For merge safety, I started with the smallest useful seam:
+  - dynamic server registry
+  - dynamic UI registry
+  - runtime validation based on registry
+  - first couple of UI consumers
+
+   One note
+   There was already an unrelated dirty change in:
+  - server/scripts/dev-watch.ts
+
+   I left that alone and did not make phase-1 changes there.
+
+   Recommended next move
+   I should keep going on this same branch and do the stabilization pass:
+   1. rerun server/ui/shared targeted tests
+   2. fix failures
+   3. run typechecks
+   4. then extend the same registry-driven approach to the next safest UI surfaces