Refactor: remove desktop/Tauri bundle, add i18n, CI/CD pipeline

- Remove desktop (Tauri) bundle: docs/desktop.md, icons/, tauri.conf.json,
  src/desktop/mod.rs, gen/schemas/
- Remove build.rs (no longer needed)
- Add i18n system (crates/core-api, plugin-mobile-connector, web)
- Refactor config system (src/config.rs, boot_format.rs)
- Add mobile connector features (app, router, device pairing)
- Plugin system improvements (skald-core)
- Update dependencies (Cargo.lock, Cargo.toml)
- CI/CD: Gitea Actions workflows (nightly + release), package.sh,
  verify-version.sh, builds.skaldagent.net config

web/components/copilot.js

@@ -389,6 +389,7 @@ export class AppCopilot extends I18nMixin(ChatSession) {
       </div>
 
       <div class="copilot-input-area">
+        ${this._renderNoModelsBanner()}
         <div class="copilot-composer"
              @dragover=${(e) => e.preventDefault()}
              @drop=${(e) => this._onDrop(e)}>
@@ -416,6 +417,7 @@ export class AppCopilot extends I18nMixin(ChatSession) {
           <textarea
             class="copilot-textarea"
             rows="1"
+            ?disabled=${this._noModels}
             placeholder=${t('chat.placeholder')}
             @keydown=${this._composerKeydown}
             @input=${(e) => { this._autoResize(e.target); this._updateCmdMenu(e.target.value); }}
@@ -469,7 +471,7 @@ export class AppCopilot extends I18nMixin(ChatSession) {
                     <i class="bi bi-stop-fill"></i>
                   </button>`
                 : nothing}
-              <button class="copilot-send-btn" @click=${() => this._send()} title=${t('chat.send')}>
+              <button class="copilot-send-btn" ?disabled=${this._noModels} @click=${() => this._send()} title=${t('chat.send')}>
                 <i class="bi bi-send-fill"></i>
               </button>
             </div>