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/web/templates/partials/sidebar.html

@@ -23,8 +23,14 @@
     </a>
     {% endif %}
     {% if can.get("folder.manage") %}
+    {# Asks for the name rather than making "New folder" and leaving somebody to
+       find the rename. `data-prompt` writes the answer into hx-vals before the
+       request goes out; see ui.js for why this is not htmx's own hx-prompt. #}
     <button class="btn btn--icon" hx-post="/api/folders" hx-swap="none"
-            hx-vals='{"name": "New folder"}' aria-label="New folder" title="New folder">
+            data-prompt="What should this folder be called?"
+            data-prompt-title="New folder" data-prompt-field="name"
+            data-prompt-label="Create"
+            aria-label="New folder" title="New folder">
       {{ icon("folder") }}
     </button>
     {% endif %}