docs: comprehensive GA pass — stable-release wording, released-spec links, install tags (#2566)

docs/migration/upgrade-to-v2.md

@@ -19,7 +19,7 @@ If you are already on v2 and want to adopt the **2026-07-28 protocol revision**,
    both `import` and `require('@modelcontextprotocol/…')` resolve natively.
 2. **Run the codemod.**
     ```bash
-    npx @modelcontextprotocol/codemod@beta v1-to-v2 .
+    npx @modelcontextprotocol/codemod@latest v1-to-v2 .
     ```
     Run it at the **package root** (`.`), not `./src` — it also rewrites `package.json`,
     and real projects import the SDK from `test/`, `scripts/`, and fixtures too.
@@ -233,10 +233,9 @@ quote-anchored pattern misses silently — match either quote. The build layout
 changed: v2 emits `.mjs`/`.cjs` siblings in a flat `dist/`, so v1's `/dist/cjs/` ↔
 `/dist/esm/` flavor-pair path swaps have no equivalent.
 
-#### Registry availability during the beta
+#### Registry availability
 
-All v2 packages are published on the public npm registry. Two notes for the beta
-window:
+All v2 packages are published on the public npm registry. Two notes:
 
 - As of `2.0.0-beta.1` all v2 packages share one version number (earlier alphas
   did not). The codemod writes ranges that match what is published, so prefer its