Remove ABID system and KVTag model - use UUIDv7 IDs exclusively

This commit completes the simplification of the ID system by:

- Removing the ABID (ArchiveBox ID) system entirely
- Removing the base_models/abid.py file
- Removing KVTag model in favor of the existing Tag model in core/models.py
- Simplifying all models to use standard UUIDv7 primary keys
- Removing ABID-related admin functionality
- Cleaning up commented-out ABID code from views and statemachines
- Deleting migration files for ABID field removal (no longer needed)

All models now use simple UUIDv7 ids via `id = models.UUIDField(primary_key=True, default=uuid7)`

Note: Old migrations containing ABID references are preserved for database
migration history compatibility.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

archivebox/core/admin_users.py

@@ -21,7 +21,7 @@ class CustomUserAdmin(UserAdmin):
             format_html(
                 '<code><a href="/admin/core/snapshot/{}/change"><b>[{}]</b></a></code> <b>📅 {}</b> {}',
                 snap.pk,
-                snap.abid,
+                str(snap.id)[:8],
                 snap.downloaded_at.strftime('%Y-%m-%d %H:%M') if snap.downloaded_at else 'pending...',
                 snap.url[:64],
             )
@@ -35,7 +35,7 @@ class CustomUserAdmin(UserAdmin):
             format_html(
                 '<code><a href="/admin/core/archiveresult/{}/change"><b>[{}]</b></a></code> <b>📅 {}</b> <b>📄 {}</b> {}',
                 result.pk,
-                result.abid,
+                str(result.id)[:8],
                 result.snapshot.downloaded_at.strftime('%Y-%m-%d %H:%M') if result.snapshot.downloaded_at else 'pending...',
                 result.extractor,
                 result.snapshot.url[:64],
@@ -62,7 +62,7 @@ class CustomUserAdmin(UserAdmin):
             format_html(
                 '<code><a href="/admin/api/apitoken/{}/change"><b>[{}]</b></a></code> {} (expires {})',
                 apitoken.pk,
-                apitoken.abid,
+                str(apitoken.id)[:8],
                 apitoken.token_redacted[:64],
                 apitoken.expires,
             )
@@ -76,7 +76,7 @@ class CustomUserAdmin(UserAdmin):
             format_html(
                 '<code><a href="/admin/api/outboundwebhook/{}/change"><b>[{}]</b></a></code> {} -> {}',
                 outboundwebhook.pk,
-                outboundwebhook.abid,
+                str(outboundwebhook.id)[:8],
                 outboundwebhook.referenced_model,
                 outboundwebhook.endpoint,
             )