Working chat: auth, connections, streaming, folders

LLeMbas now runs end to end. Register, add an OpenAI-compatible
connection, and hold a real streaming conversation organised into
folders. Verified against the local llama-swap instance.

Streaming is the one genuinely tricky part. Sending a message returns
two HTML fragments -- the user bubble and an empty assistant bubble
carrying an sse-connect -- and that attribute is the ONLY thing that
starts a generation. Rendering an incomplete assistant message as a
streaming shell falls out of the same template, which means loading a
page whose last reply never finished simply picks it up again.

Details worth knowing about, each commented where it matters:

- SSE payloads are split across several data: lines. A raw newline in
  one data: line truncates the event, which shows up the first time a
  model emits a code block.
- Markdown is rendered server-side by the same helper for both the page
  and the final streamed frame, so the two cannot disagree. The fence
  renderer is replaced outright rather than using markdown-it's
  highlight option, which re-wraps output in a second <pre>.
- escape_text is html.escape, not nh3.clean_text: it escapes character
  by character, so escaping stream chunks separately equals escaping
  the whole string.
- The stream opens its own session via session_scope(); it outlives the
  request handler and the dependency-scoped session may be closed.
- Deleting a folder keeps the chats inside it (FK is SET NULL). Losing
  a conversation to a mis-clicked folder delete is unforgivable.
- Login failures use one message for "no such account" and "wrong
  password" so the form cannot enumerate registered addresses.

Also adds deploy/ for the gamebox install at https://chat.lan: system
unit, nginx vhost with buffering off (buffering on turns streaming into
one lump at the end), and install/update scripts following the same
service-user and /srv bind-mount conventions as llama-swap and comfyui.

70 tests, ruff clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scripts/build_artwork.py

@@ -35,6 +35,11 @@ except ImportError:  # pragma: no cover - design-time tool
 
 ROOT = Path(__file__).resolve().parent.parent
 ASSETS = ROOT / "assets"
+STATIC_IMG = ROOT / "src" / "lembas" / "web" / "static" / "img"
+
+# assets/ holds the design masters; the application serves its own copies from
+# static/. These are the few the running app actually needs.
+SERVED_BY_APP = ("favicon.svg", "logo-mark.svg", "banner.svg")
 
 FONT_SEMIBOLD = Path("/usr/share/fonts/adobe-source-serif/SourceSerif4Display-Semibold.otf")
 FONT_ITALIC = Path("/usr/share/fonts/adobe-source-serif/SourceSerif4Display-It.otf")
@@ -463,10 +468,18 @@ def main() -> None:
     args = parser.parse_args()
 
     args.out.mkdir(parents=True, exist_ok=True)
+    STATIC_IMG.mkdir(parents=True, exist_ok=True)
+
     for filename in args.only or BUILDERS:
+        content = BUILDERS[filename]()
         path = args.out / filename
-        path.write_text(BUILDERS[filename](), encoding="utf-8")
-        print(f"wrote {path.relative_to(ROOT)} ({path.stat().st_size:,} bytes)")
+        path.write_text(content, encoding="utf-8")
+        print(f"wrote {path.relative_to(ROOT)} ({len(content.encode()):,} bytes)")
+
+        if filename in SERVED_BY_APP:
+            served = STATIC_IMG / filename
+            served.write_text(content, encoding="utf-8")
+            print(f"      -> {served.relative_to(ROOT)}")
 
 
 if __name__ == "__main__":