feat(docker): link to container attach from the Create New tab

Attaching lived only on the Docker tab, but the place users look for anything
container-shaped is the "Run in an isolated Docker container" checkbox on Create
New. A feature nobody can find is a feature nobody has.

Adds a one-click link there that switches to the Docker tab, turns the toggle on
and focuses the container field. Reuses switchCaseModalTab and the existing sync
helper; no new CSS.

src/web/public/index.html

@@ -2629,6 +2629,7 @@
             <div class="form-row docker-quick-row">
               <label class="checkbox-row"><input type="checkbox" id="newCaseDocker"> 🐳 Run in an isolated Docker container</label>
               <span class="form-hint">Runs this case in a hardened, isolated container. The base image is built automatically on first use. Docker/Podman must be installed.</span>
+              <span class="form-hint">Already have a container running? <button type="button" class="btn-inline-check" id="dockerAdoptJumpBtn">Attach to it instead</button> — Codeman only <code>docker exec</code>s in and never touches its lifecycle.</span>
             </div>
             <details class="advanced-options docker-quick-settings" id="dockerQuickSettings">
               <summary><svg class="set-adv-chev" width="12" height="12" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2.4" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="M6 9l6 6 6-6"/></svg><span>Container settings (optional, sensible defaults)</span></summary>

src/web/public/session-ui.js

@@ -2341,6 +2341,8 @@ Object.assign(CodemanApp.prototype, {
     if (adoptToggle) adoptToggle.onchange = () => this._syncDockerAdoptMode();
     const adoptCheck = document.getElementById('dockerAdoptCheckBtn');
     if (adoptCheck) adoptCheck.onclick = () => this._dockerAdoptPreflight();
+    const adoptJump = document.getElementById('dockerAdoptJumpBtn');
+    if (adoptJump) adoptJump.onclick = () => this.jumpToDockerAdopt();
     this._syncDockerAdoptMode();
     // Scroll-into-view on focus for mobile keyboard visibility
     modal.querySelectorAll('input[type="text"]').forEach(input => {
@@ -2913,6 +2915,20 @@ Object.assign(CodemanApp.prototype, {
     else modal.removeAttribute('data-docker-adopt');
   },
 
+  /**
+   * Cross-link from the Create New tab's "Run in an isolated Docker container"
+   * row. Adoption lives on the Docker tab, but the place users actually look for
+   * anything container-shaped is that checkbox, so this jumps them there with the
+   * toggle already on rather than leaving the feature undiscoverable.
+   */
+  jumpToDockerAdopt() {
+    this.switchCaseModalTab('case-docker');
+    const toggle = document.getElementById('dockerAdoptExisting');
+    if (toggle) toggle.checked = true;
+    this._syncDockerAdoptMode();
+    document.getElementById('dockerContainerName')?.focus();
+  },
+
   /**
    * Read-only preflight against an existing container. It links nothing, so the
    * user can find out "not running" / "no tmux" / "codex present, claude missing"