fix: security hardening, macOS aria2 lookup, aria2 stability and UI bugs

[mogurt]

Summary

Fixes from a full review of the app, one commit per area:

• Security
  • Remote filenames (URL path, Content-Disposition, Civitai metadata) are reduced to a safe basename, so they can no longer escape the target directory via ../, \, drive prefixes or reserved names.
  • create_download / check_file_exists reject unsafe names.
  • Civitai / Hugging Face hosts are matched exactly (or by subdomain) instead of by substring, so API tokens are never sent to look-alike domains such as civitai.com.evil.net.
  • Token-like query params are redacted from backend logs and forwarded aria2 output.
• macOS
  • The bundled aria2 sidecar is looked up next to the main executable (where Tauri puts externalBin) instead of only in Resources/binaries.
  • Hardcoded \ path joins are replaced by joinPath / getModelBaseDir.
  • The Workflow page now uses the default <comfyui_root>/models dir like the other pages.
• UI bugs
  • The Civitai model type is no longer always empty (serde rename mismatch).
  • Changing the URL no longer downloads under the previous URL's filename and folder; stale parse results are discarded.
  • Settings inputs no longer drop characters or push half-typed proxy URLs to aria2 (state updates synchronously; DB writes and aria2 sync are debounced).
• Dependencies
  • Removed the unused react-router-dom.
  • Moved shadcn to devDependencies. npm audit now reports 0 vulnerabilities, down from 17.
• aria2 stability
  • Startup retries with a fresh port and retries the RPC connection with backoff.
  • Websocket connections are versioned, so a stale socket can't tear down the current one and events aren't emitted twice after reconnects.
  • After an automatic restart, the app reconnects and re-applies runtime settings, and the crash counter resets after stable running.
  • Polling reconciles tasks aria2 no longer reports, so they can't get stuck in "downloading".
  • --no-conf is set, --rpc-allow-origin-all is dropped, and exit waits at most 2s for aria2.
• Build: aria2 from pinned official release
  • The macOS binaries came from AnInsomniacy/aria2-builder, which now returns 404 and broke npm ci on macOS. That breaks all CI, including main.
  • aria2 is pinned to 1.37.0 and every download is SHA256-verified. The hashes are cross-checked against the Homebrew and Scoop package definitions.
  • macOS builds the official source using system frameworks only (AppleTLS), then checks with otool that it links nothing from Homebrew.
  • Windows uses the official GitHub release zip.
  • Removed the silent fallback that bundled a PATH aria2c (Homebrew-linked, broken on users' machines).
  • ARIA2C_PATH can override the binary, and CI caches it.
• Release automation
  • release-please ran only on the stale dev branch; it now runs on main, with bootstrap-sha set because the v0.1.0 tag is not in main's history.
  • When release-please creates a release, it calls release.yml (now workflow_call-able) to build the installers. This is needed because tags pushed with GITHUB_TOKEN don't trigger workflows.
• Page title changed from temp_scaffold to ComfyDownloader.

Testing

• npm run lint (0 errors; 1 existing warning in TaskList.tsx)
• npm run typecheck
• cd src-tauri && cargo test: 18 passed, including new tests for filename sanitizing, host matching and URL redaction
• cargo fmt --check, npm run build, npm audit

Manual end-to-end test on Windows (tauri dev, driven through the real UI):

• Downloaded 4 models from Hugging Face and Civitai (24 KB to 319 MB). All were auto-routed to the right folder, and all hashes match upstream (SHA256 / git blob).
• Pausing a 319 MB download at 125 MB and resuming continued from the partial file and completed.
• Re-downloading an existing file was skipped under the skip strategy.
• Switching URLs while a parse was in flight showed only the new URL's result.
• Fast typing into settings dropped no characters, and the value persisted.
• Killing aria2c triggered an automatic restart and reconnect with no duplicate events.
• Traversal filenames (../../x, ..\x.dll, C:\x) were rejected via real IPC, and nothing was written outside the target dir.