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>

tests/test_crypto.py

@@ -0,0 +1,67 @@
+"""Secret encryption and password hashing."""
+
+from __future__ import annotations
+
+from lembas.security.passwords import (
+    hash_password,
+    validate_password,
+    verify_password,
+)
+from lembas.services.crypto import decrypt, encrypt, mask
+
+
+def test_encrypt_round_trip():
+    secret = "sk-proj-abcdef1234567890"
+    assert decrypt(encrypt(secret)) == secret
+
+
+def test_encrypt_is_not_reversible_by_eye():
+    secret = "sk-proj-abcdef1234567890"
+    assert secret not in encrypt(secret)
+
+
+def test_encrypt_is_randomised():
+    """Fernet includes a random IV, so the same input must not repeat."""
+    assert encrypt("same") != encrypt("same")
+
+
+def test_empty_secret_stays_empty():
+    """Endpoints that need no key store nothing, not an encrypted blank."""
+    assert encrypt("") == ""
+    assert decrypt("") == ""
+
+
+def test_decrypt_fails_soft_on_garbage():
+    """An unreadable value means the secret key changed. The admin UI has to
+    stay usable so the key can simply be re-entered."""
+    assert decrypt("not-a-valid-token") == ""
+
+
+def test_mask_keeps_enough_to_identify_but_not_to_use():
+    masked = mask("sk-proj-abcdef1234567890")
+    assert masked.startswith("sk-")
+    assert masked.endswith("7890")
+    assert "abcdef" not in masked
+
+
+def test_mask_hides_short_secrets_entirely():
+    assert set(mask("short")) == {"*"}
+
+
+def test_password_round_trip():
+    stored = hash_password("speak-friend")
+    assert verify_password("speak-friend", stored)
+    assert not verify_password("Speak-Friend", stored)
+
+
+def test_password_hash_is_salted():
+    assert hash_password("same") != hash_password("same")
+
+
+def test_verify_rejects_a_corrupt_hash_instead_of_raising():
+    assert not verify_password("anything", "not-a-hash")
+
+
+def test_short_passwords_are_rejected():
+    assert validate_password("short") is not None
+    assert validate_password("long-enough-password") is None