pi session context persistence, fix new session button, add clear all sessions

- handle pi process death by nulling piProcess ref so next message respawns
- replay conversation history on respawn via --session flag
- fix user message JSONL format to array for pi compatibility
- fix container sessions mount to match storage path
- fix ChatPanelWrapper: key on inner component so usePiChat resets on new session
- add bulk delete sessions endpoint and clear all button in chat header

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/servers/api/pi/storage.ts

@@ -129,7 +129,7 @@ export function messagesToJnlEntries(messages: Message[], meta: SessionMeta): Jn
         id,
         parentId: prevId,
         timestamp: new Date(msg.timestamp).toISOString(),
-        message: { role: 'user', content: msg.text ?? '' },
+        message: { role: 'user', content: [{ type: 'text' as const, text: msg.text ?? '' }] },
       };
       entries.push(entry);
       prevId = id;
@@ -281,11 +281,16 @@ export function jnlEntriesToMessages(entries: JnlEntry[]): ParsedSession {
     const ts = new Date(entry.timestamp).getTime();
 
     if (msgEntry.message.role === 'user') {
+      const rawContent = msgEntry.message.content;
+      const text =
+        typeof rawContent === 'string'
+          ? rawContent
+          : (rawContent as Array<JnlTextContent>).map((c) => c.text).join('\n');
       messages.push({
         id: entry.id,
         timestamp: ts,
         role: 'user',
-        text: msgEntry.message.content as string,
+        text,
       });
     } else if (msgEntry.message.role === 'assistant') {
       const contentBlocks = msgEntry.message.content as Array<JnlTextContent | JnlToolCall>;
@@ -380,6 +385,15 @@ function metaToIndexEntry(meta: SessionMeta, relFile: string): SessionIndexEntry
   };
 }
 
+// ── Path resolution ─────────────────────────────────────────────────────
+
+export async function getSessionFilePath(baseCwd: string, sessionId: string): Promise<string | null> {
+  const index = await loadIndex(baseCwd);
+  const entry = index[sessionId];
+  if (!entry) return null;
+  return path.join(getSessionsDir(baseCwd), entry.file);
+}
+
 // ── Session CRUD ───────────────────────────────────────────────────────
 
 export async function saveSession(