chore(frontend): remove the legacy vanilla-JS frontend and its tooling

The SvelteKit app under /frontend has fully superseded the legacy
vanilla-JS/CSS frontend in /static, which was only ever served by a
debug `cargo run` / `PROFILE=dev` and never shipped to production.
Remove it together with the whole subsystem that existed only to
support it (~54k lines).

Frontend & assets:
- Delete /static (js/, css/, *.html, sw.js, basemaps/, locales symlink).
- Relocate the brand/PWA assets (logo/, favicon.ico, manifest.webmanifest)
  to frontend/static/ so they ship with the SPA. This also fixes the
  favicon, which app.html referenced but was missing from the prod bundle.
- Migrate the Nextcloud login-flow redirects from /nextcloud-error.html
  to the SvelteKit /nextcloud/error route.

Web layer:
- Simplify resolve_static_path: drop the PROFILE=dev branch; always prefer
  the Vite static-dist/ build, fall back to the configured path.
- Resolve i18n locales from the served SPA dir with a frontend/static
  fallback so `just dev` works without a prior build.

Build:
- Prune build.rs from 1262 to ~70 lines (git metadata only); the Rust asset
  pipeline and the OXICLOUD_RUST_ASSETS rollback flag are gone.
- Drop the now-unused build-dependencies (oxc_*, lightningcss).
- Remove the COPY static lines from the Dockerfile (cacher + builder).

Tooling & docs:
- Delete biome.json, jsconfig.json, tools/check-*.py, identifier.sh.
- Remove the legacy front-* justfile recipes; repoint the design-system
  scripts (locales, dead-tokens, brand-drift, token-docs) at the frontend,
  and drop check-contrast/check-headings (coupled to the old token
  taxonomy / multi-page HTML).
- Repoint docs/DESIGN-SYSTEM.md links; remove 5 superseded docs/plan/*.

Backend dead code:
- Remove the dead `folder_repo` field from FileBlobWriteRepository.
- Remove the deprecated GET /api/folders/{id}/listing endpoint
  (superseded by /resources).

Verified: cargo clippy (all-features/all-targets) clean, cargo test
--workspace 448 passed, cargo fmt clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/infrastructure/repositories/pg/file_blob_write_repository.rs

@@ -19,7 +19,6 @@ use crate::common::errors::DomainError;
 use crate::domain::entities::file::File;
 use crate::domain::services::path_service::StoragePath;
 
-use super::folder_db_repository::FolderDbRepository;
 use super::transaction_utils::retry_on_deadlock;
 use crate::infrastructure::services::dedup_service::DedupService;
 
@@ -27,11 +26,6 @@ use crate::infrastructure::services::dedup_service::DedupService;
 pub struct FileBlobWriteRepository {
     pool: Arc<PgPool>,
     dedup: Arc<DedupService>,
-    /// Retained on the struct after D0-8 inlined parent-folder lookups
-    /// directly via SQL; kept for now so D0's diff stays scoped to drive_id
-    /// + provenance plumbing. Slated for removal in a follow-up cleanup.
-    #[allow(dead_code)]
-    folder_repo: Arc<FolderDbRepository>,
     /// Shared handle to `FileBlobReadRepository`'s file_id → blob_hash
     /// cache. Content swaps and hard deletes invalidate the mapping here
     /// so the read side can never serve a stale blob after a PUT update.
@@ -42,13 +36,11 @@ impl FileBlobWriteRepository {
     pub fn new(
         pool: Arc<PgPool>,
         dedup: Arc<DedupService>,
-        folder_repo: Arc<FolderDbRepository>,
         hash_cache: Cache<String, String>,
     ) -> Self {
         Self {
             pool,
             dedup,
-            folder_repo,
             hash_cache,
         }
     }
@@ -65,7 +57,6 @@ impl FileBlobWriteRepository {
                     .unwrap(),
             ),
             dedup: Arc::new(DedupService::new_stub()),
-            folder_repo: Arc::new(super::folder_db_repository::FolderDbRepository::new_stub()),
             hash_cache: Cache::builder().max_capacity(10_000).build(),
         }
     }