feat: add versioning

AGENTS.md

@@ -218,3 +218,26 @@ When behavior changes:
 If a product decision would materially affect persistence compatibility,
 GitHub writes, AI data exposure, destructive behavior, or default keybindings,
 ask the repository owner rather than guessing.
+
+## Semantic versioning
+
+The application version lives in `version.go` and must use Semantic Versioning
+in `MAJOR.MINOR.PATCH` form.
+
+- Keep the major version at `0` until the repository owner explicitly requests
+  a `1.0.0` or later release.
+- Increment `MINOR` and reset `PATCH` to zero for a completed new
+  backward-compatible feature. During `0.x`, also use a minor increment for an
+  intentional breaking change and document that break.
+- Increment `PATCH` for a completed backward-compatible bug fix, refinement,
+  or other non-feature change.
+- Apply one version increment per complete logical change, not per user prompt.
+  Follow-up questions and refinements that finish the same feature share that
+  feature's single version increment.
+- Before incrementing, determine the logical change boundary from the
+  conversation and current work. When the boundary is unclear and Jujutsu is
+  available, inspect the current change and its parent read-only; an empty
+  described parent may identify the feature being developed. Never mutate
+  Jujutsu history merely to determine a version.
+- If the current logical change already contains the appropriate version
+  increment, do not increment it again for another prompt in that same change.