docs: restructure docs into diataxis (#121)

docs/how-to/projects.md

@@ -0,0 +1,57 @@
+# Projects
+
+Projects let you route messages to repos from anywhere using `/alias`.
+
+## Register a repo as a project
+
+```sh
+cd ~/dev/happy-gadgets
+takopi init happy-gadgets
+```
+
+This adds a project to your config:
+
+```toml
+[projects.happy-gadgets]
+path = "~/dev/happy-gadgets"
+```
+
+## Target a project from chat
+
+Send:
+
+```
+/happy-gadgets pinky-link two threads
+```
+
+## Project-specific settings
+
+Projects can override global defaults:
+
+```toml
+[projects.happy-gadgets]
+path = "~/dev/happy-gadgets"
+default_engine = "claude"
+worktrees_dir = ".worktrees"
+worktree_base = "master"
+```
+
+If you expect to edit config while Takopi is running, enable hot reload:
+
+```toml
+watch_config = true
+```
+
+## Set a default project
+
+If you mostly work in one repo:
+
+```toml
+default_project = "happy-gadgets"
+```
+
+## Related
+
+- [Context resolution](../reference/context-resolution.md)
+- [Worktrees](worktrees.md)
+