A folder that carries something, and a way to name one

A folder was a name and nothing else -- and not even that, since PATCH could
rename one and nothing in the interface ever called it. It now carries a
description, a system prompt, and seeds for the model, the kind and the agent
target, with a settings page behind the row.

The prompt is a fourth rung on the ladder, chat > folder > model > instance,
and it goes above the model deliberately: a model's prompt describes the model
wherever it is used, a folder's describes this piece of work whichever model
is pointed at it. It is read when a reply is built rather than copied when a
chat is made, so editing it reaches the chats already there, and the walk up
the parents is bounded and cycle-safe because it runs on the request path.
`api/pages.py` mirrors the ladder for the settings panel and had to gain the
same rung -- a panel naming the wrong source is worse than one naming none,
because it is believed.

The seeds fill in what the request left empty and nothing it filled in: the
folder says what this work usually needs, the screen in front of somebody says
what they want this time. `ssh_profile_id` is a plain string rather than a
foreign key, for the reason `compacted_through_id` is, so it is validated on
read.

Getting *into* a folder needed fixing too. `/api/chats/start` has accepted a
folder_id since folders existed and nothing ever sent one, so the only route in
was to make the chat elsewhere and move it. There is a New chat here on the row
now, and `?folder=` on the new-chat screen.

Naming is a themed dialog, and deliberately not htmx's hx-prompt: htmx calls
the browser's prompt() synchronously and only then fires htmx:prompt with the
answer already in hand, so intercepting the event cannot supply a different one
and the grey box appears anyway. `data-prompt` follows the data-confirm-button
shape instead -- swallow the click, ask, write the answer into hx-vals,
click again behind a guard. JSON.stringify rather than concatenation, or a
folder called `"` produces hx-vals that does not parse and the rename silently
does nothing. Driven under a DOM stub, and there is a test that no template
brings hx-prompt back.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/lembas/api/chats.py

@@ -21,6 +21,7 @@ from lembas.db.models import (
     ROLE_ASSISTANT,
     ROLE_USER,
     Chat,
+    Folder,
     Message,
     Model,
     User,
@@ -95,7 +96,25 @@ def _new_chat(
     offered the control -- by which point the model had already answered under
     the wrong rules. The reasoning effort is accepted for the same reason, and
     wins over the model's default: an explicit choice beats an inherited one.
+
+    A folder's own defaults fill in anything the request left empty, and nothing
+    it filled in. That order is the point: the folder says what this piece of
+    work usually needs, and the screen in front of somebody says what they want
+    this time. The folder's system prompt is deliberately not among them -- it
+    is read at request time so that editing the folder later reaches the chats
+    already in it.
     """
+    folder = db.get(Folder, folder_id) if folder_id else None
+    if folder is not None and folder.user_id != user.id:
+        folder = None
+    if folder is not None:
+        model_id = model_id or folder.model_id
+        kind = kind or folder.kind
+        if kind == KIND_AGENT:
+            ssh_profile_id = ssh_profile_id or folder.ssh_profile_id
+            project_dir = project_dir or folder.project_dir
+            agent_mode = agent_mode or folder.agent_mode
+
     chosen = None
     if model_id:
         match = next(