fix: correct broken links, stale versions, and dead references in docs

- README: fix LICENSE link, remove dead doc links, update install
  instructions, remove hardcoded version/bundle size/LOC metrics
- artifacthub-pkg.yml: fix appVersion 0.2.18 → 0.2.20, fix README
  path, fix build-from-source cd path
- docs/README.md: trim to only reference files that actually exist
  (was 160 lines of aspirational links, now 47 lines of real ones)
- CLAUDE.md: correct "no MUI imports" claim — code uses @mui/material
- headlamp-plugin-developer agent: match corrected MUI convention

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

artifacthub-pkg.yml

@@ -7,7 +7,7 @@ createdAt: "2026-02-12T00:00:00Z"
 description: A comprehensive Headlamp plugin for managing Bitnami Sealed Secrets with client-side encryption and RBAC-aware UI
 license: Apache-2.0
 homeURL: https://github.com/privilegedescalation/headlamp-sealed-secrets-plugin
-appVersion: 0.2.18
+appVersion: 0.2.20
 containersImages:
   - name: sealed-secrets-controller
     image: docker.io/bitnami/sealed-secrets-controller:v0.24.0
@@ -51,7 +51,7 @@ install: |
   #### Option 2: Build from Source
   ```bash
   git clone https://github.com/privilegedescalation/headlamp-sealed-secrets-plugin
-  cd headlamp-sealed-secrets-plugin/headlamp-sealed-secrets
+  cd headlamp-sealed-secrets-plugin
   npm install
   npm run build
   ```
@@ -69,7 +69,7 @@ install: |
   - Manage sealing keys
   - Configure controller settings
 
-  For detailed usage instructions, see the [README](https://github.com/privilegedescalation/headlamp-sealed-secrets-plugin/blob/main/headlamp-sealed-secrets/README.md).
+  For detailed usage instructions, see the [README](https://github.com/privilegedescalation/headlamp-sealed-secrets-plugin/blob/main/README.md).
 maintainers:
   - name: privilegedescalation
     email: privilegedescalation@users.noreply.github.com