Add multi-user auth, settings area, and unified label feed

Turns Daybook into a multi-user tool and reworks the feed UI:

- Multi-user: Django session login (username/password + remember-me),
  per-user personal API tokens (DRF authtoken), whole app gated behind
  login. Each artifact has an owner; feeds are private per user.
- Rename persona -> source (free-text label for whatever posted an
  artifact: agent-profile, script, or person). source + tags form one
  unified label system; single label filter matches tags, source has
  its own filter/column/sidebar.
- Settings area (gear/user menu, top-right): Account (view/regenerate
  token) and Demo Data (in-app button seeding one artifact per kind).
  User account management via Django admin (superusers only).
- Feed rework: rolling 7-day window with sticky inline date separators
  and infinite scroll; left sidebar is now a Sources list with per-source
  unread counts; artifact type shown as text after title; source in its
  own column.
- Unread tracking: read_at on Artifact, marked read when previewed,
  bold titles for unread, sidebar unread badges, old banner removed.
- Tag colours: global shared registry, hash-based default with optional
  per-tag override via tag_colors on POST/PATCH.
- Ingest: token resolves owner; same source name under two users' tokens
  stays isolated. daybook_post.py renamed persona->source, requires a
  real token, --check accepts a bearer token. Docs updated to match.

Migrations 0004-0008 rename persona, add owner (nullable -> backfill to
first superuser -> required), and add read_at. Fresh installs no-op the
backfill.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

artifacts/demo_data.py

@@ -0,0 +1,87 @@
+"""Sample artifact content for the Settings -> Demo Data button.
+
+Creates one artifact of every supported kind, owned by the requesting user,
+tagged "demo", with source "demo".
+"""
+
+SOURCE = "demo"
+
+TEXT_SAMPLES = [
+    (
+        "markdown",
+        "Seed: Markdown Sample",
+        "# Markdown Sample\n\nThis is a **seed** artifact demonstrating markdown rendering.\n\n- item one\n- item two\n",
+        "markdown",
+    ),
+    (
+        "html_fragment",
+        "Seed: HTML Fragment Sample",
+        "<h2>HTML Fragment</h2><p>This is a seed HTML fragment artifact.</p>",
+        "html-fragment",
+    ),
+    (
+        "html_full",
+        "Seed: Full HTML Sample",
+        "<!doctype html><html><head><title>Seed Full HTML</title></head>"
+        "<body><h1>Full HTML Doc</h1><p>Seed artifact.</p></body></html>",
+        "html-full",
+    ),
+    (
+        "deck",
+        "Seed: Deck Sample",
+        "<section><h1>Slide One</h1><p>Seed deck artifact.</p></section>"
+        "<section><h1>Slide Two</h1><p>More content.</p></section>",
+        "deck",
+    ),
+]
+
+SEED_PNG_BYTES = bytes.fromhex(
+    "89504e470d0a1a0a0000000d494844520000000100000001080600000"
+    "01f15c4890000000a49444154789c6360000002000155e59a1a0000000049454e44ae426082"
+)
+
+SEED_PDF_BYTES = (
+    b"%PDF-1.1\n1 0 obj<</Type/Catalog/Pages 2 0 R>>endobj\n"
+    b"2 0 obj<</Type/Pages/Kids[3 0 R]/Count 1>>endobj\n"
+    b"3 0 obj<</Type/Page/Parent 2 0 R/MediaBox[0 0 200 200]>>endobj\n"
+    b"trailer<</Root 1 0 R>>\n"
+)
+
+SEED_BIN_BYTES = b"\x00\x01\x02\x03seed-binary-data\xff\xfe"
+
+BINARY_SAMPLES = [
+    ("Seed: Image Sample", "seed_pixel.png", "image/png", SEED_PNG_BYTES, "image"),
+    ("Seed: PDF Sample", "seed_doc.pdf", "application/pdf", SEED_PDF_BYTES, "pdf"),
+    ("Seed: Binary Sample", "seed_data.bin", "application/octet-stream", SEED_BIN_BYTES, "binary"),
+]
+
+
+def create_demo_artifacts(user, request):
+    from django.core.files.uploadedfile import SimpleUploadedFile
+
+    from .views import create_binary_artifact, create_text_artifact
+
+    created = 0
+    for kind, title, content, tag in TEXT_SAMPLES:
+        data = {
+            "source": SOURCE,
+            "title": title,
+            "kind": kind,
+            "content": content,
+            "tags": ["demo", tag],
+        }
+        create_text_artifact(data, request, user)
+        created += 1
+
+    for title, filename, content_type, file_bytes, tag in BINARY_SAMPLES:
+        uploaded = SimpleUploadedFile(filename, file_bytes, content_type=content_type)
+        data = {
+            "source": SOURCE,
+            "title": title,
+            "file": uploaded,
+            "tags": ["demo", tag],
+        }
+        create_binary_artifact(data, user)
+        created += 1
+
+    return created