feat(FN-3565): add plugin management CLI, loader, runner, and dashboard rou

This merge adds a complete plugin management system to Fusion: a new `fn plugin` CLI command for installing/removing plugins, a plugin loader in core, a plugin runner in engine, and dashboard routes for plugin management UI, along with a plugin management guide in docs. It also documents task evalua

Fusion-Task-Id: FN-3565

docs/plugin-management.md

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+# Plugin Management Guide
+
+[← Docs index](./README.md)
+
+This guide is the canonical end-user workflow for managing Fusion plugins across the full lifecycle: discover, install, enable/disable, configure, use, update, uninstall, and troubleshoot.
+
+> Plugin author/developer details (manifest, SDK APIs, hooks, routes, and runtime implementation) live in [Plugin Authoring](./PLUGIN_AUTHORING.md).
+
+## 1) Plugin basics
+
+Fusion uses two plugin surfaces in Settings:
+
+- **Fusion Plugins** (`Settings → Plugins → Fusion Plugins`): extend Fusion behavior (tools, routes, UI slots/views, runtimes)
+- **Pi Extensions** (`Settings → Plugins → Pi Extensions`): manage pi extension packages/sources
+
+These are related but different systems; do not treat Pi Extensions as Fusion Plugins.
+
+### Lifecycle states
+
+| State | Meaning |
+|---|---|
+| `installed` | Registered but not started yet |
+| `started` | Loaded and active |
+| `stopped` | Disabled/stopped |
+| `error` | Failed to load or failed at runtime |
+
+### Common locations
+
+| Location | Purpose |
+|---|---|
+| `~/.fusion/plugins/` | Default local plugin install location |
+| Bundled plugin manifests (shipped with Fusion) | Discoverable/installable from Plugin Manager |
+| Custom local path (absolute path) | Install plugin from a local directory |
+
+## 2) Discover available plugins
+
+### Dashboard
+
+1. Open **Settings → Plugins → Fusion Plugins**.
+2. Review bundled entries in **Bundled Plugins** and currently installed entries.
+3. Check each plugin’s status/state in the manager.
+
+Expected outcome: You can see what is already installed, what is bundled and available, and each plugin’s current lifecycle state.
+
+### CLI
+
+1. Run:
+   ```bash
+   fn plugin list
+   ```
+2. Review installed plugin IDs and status.
+
+Expected outcome: You have a terminal view of installed plugins for scripting/remote workflows.
+
+## 3) Install plugins
+
+### Install bundled plugin (dashboard)
+
+1. Go to **Settings → Plugins → Fusion Plugins**.
+2. In **Bundled Plugins**, click **Install** for the plugin.
+
+Expected outcome: Plugin is registered and appears with an initial state (typically `installed` then `started` when enabled/loaded).
+
+### Install from local path (dashboard)
+
+1. Go to **Settings → Plugins → Fusion Plugins**.
+2. Use **Install** and provide an absolute plugin path.
+3. Confirm installation.
+
+Expected outcome: Plugin is added to your local plugin set and appears in the manager.
+
+### Install from local path (CLI)
+
+1. Run:
+   ```bash
+   fn plugin install <path>
+   ```
+2. Confirm the plugin appears in:
+   ```bash
+   fn plugin list
+   ```
+
+Expected outcome: Plugin is installed from the specified path and visible in plugin listings.
+
+## 4) Enable, disable, and reload plugins
+
+### Dashboard
+
+1. Open **Settings → Plugins → Fusion Plugins**.
+2. Toggle plugin enable/disable controls.
+3. Use reload controls when available.
+
+Expected outcome: Plugin transitions between runtime states (`started` / `stopped`) and reflects transitions in the manager.
+
+### CLI
+
+```bash
+fn plugin enable <id>
+fn plugin disable <id>
+```
+
+Expected outcome: Plugin is enabled or disabled by ID.
+
+## 5) Configure plugin settings
+
+1. Go to **Settings → Plugins → Fusion Plugins**.
+2. Open the plugin settings editor (gear/settings action).
+3. Update fields and save.
+
+Expected outcome: Plugin-defined settings are persisted and used by that plugin at runtime.
+
+## 6) Verify plugin is working
+
+After installing/enabling, verify success signals relevant to that plugin:
+
+- New agent tools become available in runtime/tooling surfaces
+- Plugin routes are reachable through plugin API paths
+- Plugin UI slots/views appear in dashboard surfaces (tabs, sections, cards, nav entries)
+- Runtime-providing plugins become available for runtime hint selection/usage
+- Plugin state remains `started` (not `error`)
+
+If you need capability-level details for a specific plugin, check its README and [Plugin Authoring](./PLUGIN_AUTHORING.md).
+
+## 7) Update plugins
+
+Fusion does not use a dedicated `fn plugin update` command. Update by reinstalling the desired plugin version/source.
+
+### Dashboard
+
+1. Reinstall from the bundled entry or updated local path.
+2. Re-check state and behavior in the plugin manager.
+
+### CLI
+
+1. Re-run install against the updated source path:
+   ```bash
+   fn plugin install <path>
+   ```
+2. Confirm with:
+   ```bash
+   fn plugin list
+   ```
+
+Expected outcome: Updated plugin build/version is installed and operational.
+
+## 8) Uninstall plugins
+
+### Dashboard
+
+1. Open **Settings → Plugins → Fusion Plugins**.
+2. Uninstall the target plugin.
+
+Expected outcome: Plugin is removed from the installed list and no longer active.
+
+### CLI
+
+1. Run:
+   ```bash
+   fn plugin uninstall <id> --force
+   ```
+2. Verify removal:
+   ```bash
+   fn plugin list
+   ```
+
+Expected outcome: Plugin is removed by ID.
+
+## 9) Dashboard vs CLI mapping
+
+| Workflow | Dashboard path | CLI command |
+|---|---|---|
+| List installed plugins | Settings → Plugins → Fusion Plugins | `fn plugin list` |
+| Install plugin | Settings → Plugins → Fusion Plugins → Install | `fn plugin install <path>` |
+| Enable plugin | Settings → Plugins → Fusion Plugins → Enable toggle | `fn plugin enable <id>` |
+| Disable plugin | Settings → Plugins → Fusion Plugins → Disable toggle | `fn plugin disable <id>` |
+| Uninstall plugin | Settings → Plugins → Fusion Plugins → Uninstall | `fn plugin uninstall <id> --force` |
+| Scaffold new plugin (authoring) | n/a (developer workflow) | `fn plugin create <name>` |
+
+## 10) Troubleshooting
+
+### Plugin is in `error` state
+
+1. Open **Settings → Plugins → Fusion Plugins** and inspect state/transition feedback.
+2. Disable then re-enable the plugin.
+3. Confirm plugin source path and dependencies are valid.
+4. If needed, uninstall and reinstall the plugin.
+
+### Plugin installed but features are not visible
+
+1. Confirm plugin state is `started`.
+2. Verify what that plugin actually contributes (tools/routes/UI/runtime) in plugin docs.
+3. Confirm you are checking the correct dashboard surface (for example nav view vs settings section vs task detail slot).
+
+### Confusion between Fusion Plugins and Pi Extensions
+
+1. Use **Fusion Plugins** for Fusion plugin lifecycle management.
+2. Use **Pi Extensions** only for pi extension sources/extensions/skills/prompts/themes.
+
+### Need implementation/API details
+
+Use [Plugin Authoring](./PLUGIN_AUTHORING.md) for manifest fields, lifecycle hook signatures, UI/runtime contribution contracts, and SDK examples.