fix: Windows path handling, light theme default, file viewer in editor, first-user admin logic

Config:
- Fixed SQLite path parsing on Windows (handle drive letters without prepending /)
- Changed default theme from dark to light
- Updated OAuth test credentials (gitea_oauth_client_id/secret)

Auth:
- First real user (excluding default admin with no password) becomes admin
- Changed user count query to exclude users without password_hash

File viewer:
- Removed separate _render_file_viewer() —

app/templates/workspaces.html

@@ -44,6 +44,7 @@
 .org-tab:hover{background:var(--bg-tertiary);color:var(--text);}
 .org-tab.active{background:var(--accent);color:#fff;border-color:var(--accent);}
 .org-tab-badge{font-size:10px;padding:0 5px;border-radius:8px;background:rgba(255,255,255,.15);}
+[data-theme="light"] .org-tab-badge{background:rgba(0,0,0,.08);}
 .search-input:focus{border-color:var(--accent);}
 </style>