docs(readme): split user and build tracks; fix release for BRAT

README interleaved plugin usage with build steps, so a user wanting only
the plugin had to read past clone/bun/build. Now two tracks: install,
config, commands, settings, note schema, issues first; build and dev
after a divider.

Also adds the standalone note (fork carries the whole upstream plugin,
stock one not needed; keys and settings are not shared) and splits the
bun requirement into tests (hard, bun:test + mock.module) vs build
(tsc + vite, node-capable).

release.yml: no tag was ever pushed, so BRAT had nothing to install.
Two defects fixed:
- prerelease flag only tripped on 'canary', so a beta tag would have
  published as stable. Now any semver prerelease tag (contains '-').
- release shipped manifest.json 0.1.0 while BRAT resolves the tag from
  manifest-beta.json 0.1.0-beta.1. Version mismatch makes BRAT
  re-download every check. Prerelease tags now ship manifest-beta.json
  as manifest.json.

.github/workflows/release.yml

@@ -25,7 +25,8 @@ jobs:
             - name: Determine prerelease status
               id: status
               run: |
-                  if [[ "${{ github.ref }}" == *"canary"* ]]; then
+                  # Any semver prerelease tag (0.1.0-beta.1, 0.8.0-canary.x, 1.0.0-rc.1) ships as a prerelease.
+                  if [[ "${{ github.ref_name }}" == *"-"* ]]; then
                   echo "prerelease=true" >> $GITHUB_OUTPUT
                   else
                   echo "prerelease=false" >> $GITHUB_OUTPUT
@@ -38,9 +39,17 @@ jobs:
 
             - name: Build
               id: build
+              env:
+                  TAG: ${{ github.ref_name }}
               run: |
                   bun install --frozen-lockfile
                   bun run build
+                  # BRAT resolves the tag from manifest-beta.json, then installs the manifest.json
+                  # shipped in that release. On a prerelease tag the two must agree, or BRAT reads
+                  # back a different version than it installed and re-downloads forever.
+                  if [[ "$TAG" == *"-"* ]]; then
+                    cp manifest-beta.json dist/manifest.json
+                  fi
                   mkdir ${{ env.PLUGIN_NAME }}
                   cp dist/main.js dist/manifest.json dist/styles.css ${{ env.PLUGIN_NAME }}
                   zip -r ${{ env.PLUGIN_NAME }}-${{ github.ref_name }}.zip ${{ env.PLUGIN_NAME }}