Add bot-driven room app UI via im.paarrot.ui state.

Bots can publish a declarative panel UI that takes over a room; user
actions are sent as im.paarrot.ui.action timeline events.

src/app/features/room-app/sanitizeRoomAppCss.ts

@@ -0,0 +1,91 @@
+/**
+ * Strip dangerous CSS constructs from bot-supplied stylesheets.
+ * Not a full CSS parser — best-effort for MVP scoped injection.
+ */
+export function sanitizeRoomAppCss(css: string): string {
+  let out = css;
+  out = out.replace(/@import\b[^;{]*;?/gi, '');
+  out = out.replace(/url\s*\(\s*['"]?\s*javascript:[^)]*\)/gi, 'url(about:blank)');
+  out = out.replace(/expression\s*\([^)]*\)/gi, 'initial');
+  out = out.replace(/-moz-binding\s*:[^;]+;?/gi, '');
+  out = out.replace(/behavior\s*:[^;]+;?/gi, '');
+  out = out.replace(/@charset\b[^;]*;?/gi, '');
+  return out;
+}
+
+/**
+ * Prefix plain selectors with a scope so bot CSS cannot escape the room app root.
+ * At-rules (@media, @supports, @keyframes) are kept with nested rules re-scoped where possible.
+ */
+export function scopeRoomAppCss(css: string, scopeSelector: string): string {
+  const sanitized = sanitizeRoomAppCss(css).trim();
+  if (!sanitized) return '';
+
+  const scopeRule = (selectors: string, body: string): string => {
+    const scoped = selectors
+      .split(',')
+      .map((s) => {
+        const sel = s.trim();
+        if (!sel) return '';
+        if (sel.startsWith(scopeSelector)) return sel;
+        return `${scopeSelector} ${sel}`;
+      })
+      .filter(Boolean)
+      .join(', ');
+    return `${scoped}{${body}}`;
+  };
+
+  const rewriteBlock = (block: string): string => {
+    const trimmed = block.trim();
+    if (!trimmed) return '';
+
+    if (trimmed.startsWith('@')) {
+      const open = trimmed.indexOf('{');
+      if (open === -1) return `${trimmed};`;
+      const header = trimmed.slice(0, open).trim();
+      const inner = trimmed.slice(open + 1);
+      // @keyframes / @font-face: keep as-is (namespaced risk is low for MVP)
+      if (/^@(keyframes|font-face)\b/i.test(header)) {
+        return `${header}{${inner}}`;
+      }
+      // @media / @supports: re-scope nested rules
+      const nested = rewriteCssChunk(inner);
+      return `${header}{${nested}}`;
+    }
+
+    const open = trimmed.indexOf('{');
+    if (open === -1) return '';
+    const selectors = trimmed.slice(0, open);
+    const body = trimmed.slice(open + 1);
+    return scopeRule(selectors, body);
+  };
+
+  const rewriteCssChunk = (chunk: string): string => {
+    const parts: string[] = [];
+    let depth = 0;
+    let start = 0;
+    for (let i = 0; i < chunk.length; i += 1) {
+      const ch = chunk[i];
+      if (ch === '{') depth += 1;
+      else if (ch === '}') {
+        depth -= 1;
+        if (depth === 0) {
+          parts.push(rewriteBlock(chunk.slice(start, i)));
+          start = i + 1;
+        }
+      }
+    }
+    return parts.filter(Boolean).join('\n');
+  };
+
+  return rewriteCssChunk(sanitized);
+}
+
+export function isAllowedRoomAppImageSrc(src: string): boolean {
+  const trimmed = src.trim();
+  return (
+    trimmed.startsWith('mxc://') ||
+    trimmed.startsWith('https://') ||
+    trimmed.startsWith('http://')
+  );
+}