feat: implement plugin architecture and application settings with Svelte UI

- Added plugin base and loader for backend extensibility
- Implemented application settings management with config persistence
- Created Svelte-based frontend with Dashboard and Settings pages
- Added API routes for plugins, tasks, and settings
- Updated documentation and specifications
- Improved project structure and developer tools

.specify/templates/plan-template.md

@@ -31,10 +31,7 @@
 
 *GATE: Must pass before Phase 0 research. Re-check after Phase 1 design.*
 
-- [ ] **Causal Validity**: Do all planned modules/components have defined Contracts (inputs/outputs/props/events) before implementation logic?
-- [ ] **Immutability**: Are architectural layers and constraints defined in Module/Component Headers?
-- [ ] **Format Compliance**: Does the plan ensure all code will be wrapped in `[DEF]` anchors?
-- [ ] **Belief State**: Is logging planned to follow the `Entry` -> `Validation` -> `Action` -> `Coherence` state transition model?
+[Gates determined based on constitution file]
 
 ## Project Structure