feat(db): add project personas and skills tables

* Introduce project_personas table with foreign keys to projects and agent_personas
* Add project_skills table with foreign key to projects and agent_skills
* Include override boolean field in agent_persona_skills and project_skills
* Update schema and migration files to reflect new tables and fields
* Enhance CORS handling to reflect request origin

llm/world_model_intro.md

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+# AMCS World Model
+
+AMCS provides a project-scoped world model containing memory, skills, guardrails, personas, and recent context.
+
+At the start of an agent or chat session:
+
+1. Identify the current project from explicit user input or the workspace.
+2. Call `list_projects` when the project has not already been confirmed.
+3. Call `bootstrap_world_model` with the explicit project name or ID.
+4. Apply every returned guardrail and effective skill before continuing.
+5. Use the default persona when present. Other linked persona manifests describe personas available on demand.
+
+Never silently choose or create a project. If no project matches, ask the user or create one only with explicit approval. Stateless clients must continue passing the project explicitly on project-scoped calls.
+
+Skills are additive by default. A linked skill with `override: true` replaces a lower-precedence skill with the same stable name. Guardrails are additive and later layers cannot weaken them.