docs(FN-1158): add comprehensive project documentation suite

- Add docs index with structured navigation and links across the new documentation set
- Document onboarding and technical foundations with getting-started and architecture guides
- Add detailed CLI and settings references plus feature guides for dashboard, tasks, workflow steps, missions, multi-project, and agents
- Add a contributing guide and polish cross-references between docs pages for discoverability
- Include dashboard screenshots for key views to provide visual context in the guides

docs/contributing.md

@@ -0,0 +1,107 @@
+# Contributing
+
+[← Docs index](./README.md)
+
+Thanks for contributing to Fusion.
+
+## Development Setup
+
+### Prerequisites
+
+- Node.js (current LTS recommended)
+- pnpm (`packageManager` is pnpm)
+- Git
+- `pi` runtime/auth configured for AI features
+
+### Install dependencies
+
+```bash
+pnpm install
+```
+
+### Build all packages
+
+```bash
+pnpm build
+```
+
+## Workspace Package Overview
+
+| Package | Purpose |
+|---|---|
+| `@fusion/core` | Shared domain types, stores, persistence, and core utilities |
+| `@fusion/dashboard` | Express API + React UI |
+| `@fusion/engine` | Scheduling, triage, execution, merge orchestration |
+| `@fusion/tui` | Ink-based terminal UI components |
+| `@gsxdsm/fusion` | Published CLI + pi extension |
+
+## Development Workflow
+
+```bash
+pnpm dev          # build + run CLI entrypoint in dev mode
+pnpm dev:ui       # dashboard dev server only
+pnpm typecheck    # workspace typechecks
+pnpm test         # workspace test suite
+pnpm build        # workspace builds
+```
+
+## Testing Requirements
+
+Use real test runs (not manual verification substitutes):
+
+```bash
+pnpm test
+pnpm test:coverage
+pnpm test:coverage:core
+pnpm test:coverage:engine
+pnpm test:coverage:cli
+pnpm test:coverage:dashboard
+```
+
+## Build Standalone Executables
+
+Fusion supports standalone binary builds through Bun compile scripts in the CLI package.
+
+```bash
+pnpm build:exe      # build host-target executable
+pnpm build:exe:all  # build multi-target executables
+```
+
+## Release Process
+
+Fusion uses Changesets + version PR workflow.
+
+- See [RELEASING.md](../RELEASING.md) for release flow details.
+- For published package behavior changes, include a changeset.
+
+## Code Signing
+
+Release binary signing setup is documented here:
+
+- [Code Signing Setup](./CODE_SIGNING.md)
+
+## Git / Commit Conventions
+
+Use task-ID-scoped conventional commits:
+
+- `feat(FN-XXX): ...`
+- `fix(FN-XXX): ...`
+- `test(FN-XXX): ...`
+- `docs(FN-XXX): ...` (for documentation-only changes)
+
+## Project Memory
+
+When enabled, agents can read/write durable project memory:
+
+- `.fusion/memory.md`
+
+Use it for reusable patterns, constraints, and pitfalls that should persist across tasks.
+
+## SQLite Test Runner Pitfall
+
+When running engine tests with Vitest and `node:sqlite`, ensure the engine Vitest config uses thread pool mode:
+
+- ✅ `pool: "threads"`
+- ❌ `pool: "vmThreads"`
+
+`node:sqlite` fails under Vitest VM contexts; using threads avoids that failure mode.