refactor(usage): fold claude-desktop into claude in the dashboard

The Desktop gateway's proxy traffic is still recorded under its own
app_type for route-takeover billing audit (the request detail panel
shows the real value), but the dashboard now folds it into `claude`
for display. A standalone "Claude Desktop" bucket only ever showed a
partial number: Desktop chat usage never passes through the proxy and
has no scannable local source, while its Code-tab sessions are just the
embedded Claude Code runtime writing into the shared ~/.claude/projects
tree — so a separate bucket misled users into reading it as Desktop's
full usage.

Backend: new `folded_app_type_sql` helper wraps the app_type column in
every dashboard read path (10 filter sites + the by-app projection) so
`= 'claude'` also matches claude-desktop and GROUP BY merges the two,
without changing bound-param counts. Dedup matching and provider-limit
checks keep exact comparison; get_request_logs folds only the WHERE
filter and keeps the raw app_type in its row projection.

Frontend: drop claude-desktop from the dashboard AppType/KNOWN_APP_TYPES
filter list, the UsageHero theme, and the now-dead appFilter locale key
in all four languages (the managed-app apps.claude-desktop label stays).

Adds test_claude_desktop_folds_into_claude_for_display.

src/i18n/locales/en.json

@@ -1386,7 +1386,6 @@
     "appFilter": {
       "all": "All",
       "claude": "Claude Code",
-      "claude-desktop": "Claude Desktop",
       "codex": "Codex",
       "gemini": "Gemini",
       "opencode": "OpenCode"

src/i18n/locales/ja.json

@@ -1386,7 +1386,6 @@
     "appFilter": {
       "all": "すべて",
       "claude": "Claude Code",
-      "claude-desktop": "Claude Desktop",
       "codex": "Codex",
       "gemini": "Gemini",
       "opencode": "OpenCode"

src/i18n/locales/zh-TW.json

@@ -1358,7 +1358,6 @@
     "appFilter": {
       "all": "全部",
       "claude": "Claude Code",
-      "claude-desktop": "Claude Desktop",
       "codex": "Codex",
       "gemini": "Gemini",
       "opencode": "OpenCode"

src/i18n/locales/zh.json

@@ -1386,7 +1386,6 @@
     "appFilter": {
       "all": "全部",
       "claude": "Claude Code",
-      "claude-desktop": "Claude Desktop",
       "codex": "Codex",
       "gemini": "Gemini",
       "opencode": "OpenCode"