feat: adopt v1.0.0 GA versioning and compatibility policy

Update docs that described pre-1.0 versioning semantics to their post-1.0
form ahead of the v1.0.0 GA cut.

Release-As: 1.0.0

Author: pmaxhogan

CLAUDE.md

@@ -18,11 +18,11 @@ type(optional-scope): short imperative summary
 
 - **Allowed types:** `feat`, `fix`, `perf`, `refactor`, `docs`, `test`,
   `build`, `ci`, `chore`, `style`, `revert`.
-- **Version impact (pre-1.0, `bump-minor-pre-major`):** `feat` -> minor
-  (0.x.0), `fix`/`perf` -> patch. A breaking change uses a `!`
-  (`feat!:` / `fix(core)!:`) or a `BREAKING CHANGE:` footer in the PR body;
-  pre-1.0 a breaking change still bumps only the **minor** (0.x.0), NOT a
-  major 1.0.0 - that is what `bump-minor-pre-major` means.
+- **Version impact (post-1.0):** `feat` -> minor (x.Y.0), `fix`/`perf` ->
+  patch. A breaking change uses a `!` (`feat!:` / `fix(core)!:`) or a
+  `BREAKING CHANGE:` footer in the PR body and bumps the **major** (X.0.0).
+  (`bump-minor-pre-major` is still set in `release-please-config.json` but
+  is inert now that the version is >= 1.0.0.)
 - Changelog-visible by default: `feat` (Features), `fix` (Bug Fixes), `perf`,
   `revert`, and `deps` (Dependencies). The rest - `docs`, `chore`, `ci`,
   `build`, `refactor`, `style`, `test` - are valid but **hidden**: a PR titled

CONTRIBUTING.md

@@ -42,7 +42,7 @@ Format:
 
 Common types:
 
-- `feat`: a new user-facing feature (bumps the minor version pre-1.0)
+- `feat`: a new user-facing feature (bumps the minor version)
 - `fix`: a bug fix (bumps the patch version)
 - `docs`: documentation only
 - `refactor`: code change that neither fixes a bug nor adds a feature
@@ -52,7 +52,7 @@ Common types:
 - `perf`: a performance improvement
 
 Breaking changes: add a `!` after the type/scope (for example `feat!:`) and / or
-a `BREAKING CHANGE:` footer. Pre-1.0, a breaking change bumps the minor version.
+a `BREAKING CHANGE:` footer. A breaking change bumps the major version.
 
 Examples:
 

design/SPEC.md

@@ -1471,7 +1471,7 @@ jobs:
           manifest-file: .release-please-manifest.json
 ```
 
-Maintains a "chore: release v0.x.y" PR with the changelog and version
+Maintains a "chore(main): release vX.Y.Z" PR with the changelog and version
 bumps. Merging the PR creates the `v*` tag, which fires `release.yml`.
 
 ### 19.3 `release.yml`