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/cli-reference.md

@@ -0,0 +1,251 @@
+# CLI Reference
+
+[← Docs index](./README.md)
+
+Fusion’s command-line interface is exposed through the `fn` command.
+
+## Global Usage
+
+```bash
+fn <command> <subcommand> [options]
+```
+
+### Global options
+
+| Option | Description |
+|---|---|
+| `--project <name>`, `-P <name>` | Target a specific registered project. |
+| `--help`, `-h` | Show help output. |
+
+### Project resolution order
+
+When `--project` is not supplied, Fusion resolves project context in this order:
+
+1. Explicit `--project` flag
+2. Default project (set via `fn project set-default <name>`)
+3. Current-directory auto-detection (`.fusion/fusion.db` lookup upward)
+
+---
+
+## `fn init`
+
+Initialize a new Fusion project in the current directory.
+
+```bash
+fn init
+fn init --name my-project --path /absolute/path/to/project
+```
+
+---
+
+## `fn dashboard`
+
+Start the web dashboard (default port `4040`).
+
+```bash
+fn dashboard
+fn dashboard --port 5050
+fn dashboard --interactive
+fn dashboard --paused
+fn dashboard --dev
+```
+
+---
+
+## `fn task`
+
+Task lifecycle and task operations.
+
+### Creation and planning
+
+```bash
+fn task create "Fix login race condition"
+fn task create "Fix bug" --attach screenshot.png --depends FN-010
+fn task plan "Design a new authentication flow"
+```
+
+### Query and logs
+
+```bash
+fn task list
+fn task show FN-001
+fn task logs FN-001 --follow --limit 50 --type tool
+```
+
+### Execution and status
+
+```bash
+fn task move FN-001 in-progress
+fn task update FN-001 2 done
+fn task log FN-001 "Updated API contract"
+fn task retry FN-001
+fn task pause FN-001
+fn task unpause FN-001
+```
+
+### Collaboration and guidance
+
+```bash
+fn task comment FN-001 "Needs stricter validation"
+fn task comment FN-001 "Reviewed with QA" --author "alex"
+fn task comments FN-001
+fn task steer FN-001 "Reuse existing auth middleware"
+```
+
+### Completion, maintenance, and history
+
+```bash
+fn task attach FN-001 ./trace.log
+fn task merge FN-001
+fn task duplicate FN-001
+fn task refine FN-001 --feedback "Add rollback handling"
+fn task archive FN-001
+fn task unarchive FN-001
+fn task delete FN-001 --force
+```
+
+### GitHub integration
+
+```bash
+fn task pr-create FN-001 --title "Fix login race" --base main
+fn task import owner/repo --labels bug --limit 10
+fn task import owner/repo --interactive
+```
+
+---
+
+## `fn project`
+
+Manage registered projects in multi-project mode.
+
+```bash
+fn project list --json
+fn project add my-app /path/to/app --isolation child-process
+fn project show my-app
+fn project info my-app
+fn project set-default my-app
+fn project detect
+fn project remove my-app --force
+```
+
+Subcommands: `list|ls`, `add`, `remove|rm`, `show`, `info`, `set-default|default`, `detect`.
+
+---
+
+## `fn node`
+
+Manage external execution nodes.
+
+```bash
+fn node list --json
+fn node add edge-runner --url https://node.example.com --api-key $NODE_API_KEY --max-concurrent 4
+fn node show edge-runner
+fn node health edge-runner
+fn node remove edge-runner --force
+```
+
+Subcommands: `list|ls`, `add`, `remove|rm`, `show|info`, `health`.
+
+---
+
+## `fn mission`
+
+Mission hierarchy operations.
+
+```bash
+fn mission create "Platform hardening" "Security and reliability initiative"
+fn mission list
+fn mission show mission_123
+fn mission delete mission_123 --force
+fn mission activate-slice slice_456
+```
+
+Subcommands: `create`, `list|ls`, `show|info`, `delete`, `activate-slice`.
+
+---
+
+## `fn agent`
+
+Agent runtime operations.
+
+```bash
+fn agent stop AGENT-001
+fn agent start AGENT-001
+fn agent mailbox AGENT-001
+fn agent import ./companies-manifest.yaml --dry-run
+```
+
+Subcommands: `stop`, `start`, `mailbox`, `import`.
+
+---
+
+## `fn message`
+
+Inter-agent/user message mailbox.
+
+```bash
+fn message inbox
+fn message outbox
+fn message send AGENT-001 "Please prioritize FN-222"
+fn message read MSG-123
+fn message delete MSG-123
+```
+
+---
+
+## `fn settings`
+
+Show and manage settings.
+
+```bash
+fn settings
+fn settings set maxConcurrent 4
+fn settings export --scope both
+fn settings import fusion-settings.json --yes
+```
+
+---
+
+## `fn git`
+
+Project git operations.
+
+```bash
+fn git status
+fn git fetch
+fn git fetch upstream
+fn git pull --yes
+fn git push --yes
+```
+
+---
+
+## `fn backup`
+
+Database backup lifecycle.
+
+```bash
+fn backup --create
+fn backup --list
+fn backup --restore .fusion/backups/fusion-2026-04-08.db
+fn backup --cleanup
+```
+
+---
+
+## Useful option flags by context
+
+| Option | Used by |
+|---|---|
+| `--port`, `-p` | `fn dashboard` |
+| `--interactive` | `fn dashboard`, `fn task import`, `fn project add` |
+| `--paused` | `fn dashboard` |
+| `--dev` | `fn dashboard` |
+| `--attach` | `fn task create` |
+| `--depends` | `fn task create` |
+| `--feedback` | `fn task refine` |
+| `--yes` | confirmation-skipping flows (`task plan`, `settings import`, git pull/push, etc.) |
+| `--limit`, `-l` | `fn task import` |
+| `--labels`, `-L` | `fn task import` |
+
+For configuration details used by these commands, see [Settings Reference](./settings-reference.md).