feature: add mkdocs-material documentation site with CI deployment

Generate comprehensive documentation for all 173 source units and
integrate mkdocs-material into the build toolchain. Documentation
covers kernel core, x86 architecture, drivers, applications, and
all subsystems with a tabbed navigation structure.

- Add mkdocs.yml with material theme, mermaid support, and tabbed nav
- Add doc/index.md landing page
- Generate doc/src/ markdown for every Pascal unit in src/
- Reorganize planning docs into doc/planning/
- Add compat, lvglh, and toolchain doc sections
- Update Dockerfile to install python3 and mkdocs-material (pinned <2)
- Replace pasdoc-based compile_docs.sh with mkdocs build --strict
- Add compile_docs.sh to the main build pipeline in compile.sh
- Add deploy-docs step in .drone.yml with host volume mount to nginx
- Add site/.gitkeep for build output directory

.drone.yml

@@ -25,6 +25,30 @@ steps:
       - chmod +x /drone/src/toolchain/*.sh
       - /drone/src/toolchain/compile.sh
       
+  - name: deploy-docs
+    image: alpine:latest
+    depends_on:
+      - compile
+    when:
+      branch:
+        - master
+        - develop
+        - feature/mkdocs
+    volumes:
+      - name: docs-htdocs
+        path: /htdocs
+    commands:
+      - apk add --no-cache rsync
+      - |
+        if [ "${DRONE_BRANCH}" = "master" ]; then
+          DEST="/htdocs/master"
+        else
+          DEST="/htdocs/develop"
+        fi
+      - mkdir -p "$DEST"
+      - rsync -a --delete site/ "$DEST/"
+      - echo "Documentation deployed to ${DRONE_BRANCH}"
+
   - name: upload-iso-artifact
     image: alpine/git
     depends_on:
@@ -63,4 +87,10 @@ steps:
         from_secret: discord_webhook_id
       webhook_token:
         from_secret: discord_webhook_secret
-      message: "**Asuro Build**\n\n{{#success build.status}}✅ Build successful!\n\n{{else}}❌ Build failed!\n\n{{/success}}Repository: `{{repo.namespace}}/{{repo.name}}`\nBranch: `{{commit.branch}}`\nCommit: `{{commit.sha}}`\nAuthor: `{{commit.author}} <{{commit.email}}>`\n\nGitea Diff: [Link](<{{commit.link}}>)\nDrone Build: [Link](<{{build.link}}>)\n\nMessage: {{commit.message}}"
+      message: "**Asuro Build**\n\n{{#success build.status}}✅ Build successful!\n\n{{else}}❌ Build failed!\n\n{{/success}}Repository: `{{repo.namespace}}/{{repo.name}}`\nBranch: `{{commit.branch}}`\nCommit: `{{commit.sha}}`\nAuthor: `{{commit.author}} <{{commit.email}}>`\n\nGitea Diff: [Link](<{{commit.link}}>)\nDrone Build: [Link](<{{build.link}}>)\n\nMessage: {{commit.message}}"
+
+volumes:
+  - name: docs-htdocs
+    host:
+      path: /mnt/user/htdocs/asuro_docs
+