feat(architecture): add multi-subproject awareness and automatic context resync

- Implemented subproject root resolution based on active editor hint
- Added debounced event listener for active editor changes to trigger chip status updates
- Updated sidebar provider to re-resolve active subproject root on every chip build
- This ensures correct architecture context is injected when working in a monorepo or multi-root-style parent folder

src/features/projectArchitecture/index.ts

@@ -130,6 +130,56 @@ export function architectureDocPathFor(projectRoot: string): string {
     return path.join(projectRoot, ARCH_DIR_REL, ARCH_FILE);
 }
 
+/**
+ * Resolve the *effective* subproject root when the user has opened a parent
+ * folder that contains several independent subprojects (each carrying its own
+ * `.astra/project-context/` or `package.json`).
+ *
+ * Walks up from `hintFsPath` toward `workspaceRoot` and returns the first
+ * ancestor that already looks like a subproject. Falls back to `workspaceRoot`
+ * when no nested marker is found, when the hint lives outside the workspace,
+ * or when the hint sits inside `node_modules` / build folders.
+ *
+ * Markers (in order):
+ *   1. `.astra/project-context/` — an already-initialised Astra subproject.
+ *   2. `package.json` — a Node project root (covers fresh subprojects that
+ *      haven't activated architecture mode yet).
+ */
+export function resolveActiveSubprojectRoot(workspaceRoot: string, hintFsPath?: string): string {
+    if (!workspaceRoot || !hintFsPath) return workspaceRoot;
+    let wsNorm: string;
+    let hintNorm: string;
+    try {
+        wsNorm = path.resolve(workspaceRoot);
+        hintNorm = path.resolve(hintFsPath);
+    } catch {
+        return workspaceRoot;
+    }
+    const rel = path.relative(wsNorm, hintNorm);
+    if (!rel || rel.startsWith('..') || path.isAbsolute(rel)) {
+        return workspaceRoot;
+    }
+    // Skip hints that live inside dependency / build folders — those are not
+    // user-authored subprojects, and `node_modules/<pkg>/package.json` would
+    // otherwise be mistaken for a subproject root.
+    const skipSegments = new Set(['node_modules', '.git', 'out', 'dist', '.astra']);
+    const relSegments = rel.split(/[\\/]+/);
+    if (relSegments.some((s) => skipSegments.has(s))) return workspaceRoot;
+
+    let cur = path.dirname(hintNorm);
+    while (true) {
+        if (cur === wsNorm) return workspaceRoot;
+        const r = path.relative(wsNorm, cur);
+        if (!r || r.startsWith('..') || path.isAbsolute(r)) return workspaceRoot;
+        const astraMarker = path.join(cur, ARCH_DIR_REL);
+        const pkgMarker = path.join(cur, 'package.json');
+        if (fs.existsSync(astraMarker) || fs.existsSync(pkgMarker)) return cur;
+        const parent = path.dirname(cur);
+        if (parent === cur) return workspaceRoot;
+        cur = parent;
+    }
+}
+
 /**
  * Backwards-compatible thin wrapper. The watcher / refresh path only needs the
  * shape-signature to decide whether to re-emit the doc, so we expose `scanProject`