Add a vault upload dialog with optional ingest and serve /api/upload-vault

[benjsmith]

The graph sidebar's + button in the vendored CE editor (edit.js) posts to /api/upload-vault, but the Switchbay daemon never served that path. In the built-in sidebar the button was handled separately and always sent one file straight to an ingest agent. In the embedded CE sidebar the request went through the /embed/ce proxy to CE's own viewer, which works for small files but fails with 413 above 1 MiB, the proxy's body limit.

This adds a daemon route for POST /api/upload-vault and a single Switchbay upload dialog that every + button opens.

Route. It follows CE's viewer_server.py handler: multipart form, every part with a filename is saved into <workspace>/vault/raw/, names are sanitised with CE's rules (basename only, anything outside [A-Za-z0-9._-] becomes _, empty or dot-leading names are refused), an existing file of the same name is replaced, and the reply is {"ok": true, "saved": [...]}. Files are streamed to a temporary file and moved into place, with a 50 MB per-file limit (413 with the names already saved). An optional ingest form field (true/false, default false) asks for the saved files to be ingested. They are queued as ingest runs on the existing drain queue, in one batch: through CE's deterministic local ingest when CE is installed, or through the ingest agent (one run per file) when CE is absent and the default model provider is ready. With neither, the files are still saved and the reply's ingest.message says why nothing was ingested. When ingest is requested the reply also carries ingest: {backend, queued, runs: [{file, run_id, vault_path}]}.

Reserved path. /api/upload-vault is added to the daemon-reserved API list, so the embedded CE sidebar's own upload also reaches this route instead of CE's viewer through the proxy, which removes the 1 MiB limit for uploads.

Dialog. UploadVaultDialog is a Switchbay React component in the shell, not part of edit.js. It lets you pick several files (and add or remove them before uploading), has an "Ingest automatically" checkbox, and uses the theme variables, so it follows light and dark mode. Switchbay has no global auto-ingest setting, so the checkbox starts off and remembers the last choice in localStorage (sy.uploadVault.ingest). After the upload a toast reports what was saved and whether ingest was queued. For agent ingest it opens the run in the Agents view, as the old + did.

Entry points. A new + in the Files browser toolbar opens the dialog. It is always there, with or without CE, so upload keeps working when the Graph tab is hidden. The built-in sidebar and Zen graph + buttons open the same dialog. CE's embed has no hook or message for its +, so the embedded CE sidebar's + is intercepted on the Switchbay side (a capture-phase click listener on the sidebar slot) and opens the dialog too. If CE's + ever runs its own handler, it posts a plain upload to the same reserved route. edit.js is unchanged. Dropping files onto the sidebar still stages them and starts ingest agents, as before.

Tests. tests/unit/test_upload_vault.py checks that the daemon resolves edit.js's literal request, and covers multi-file uploads, same-name replacement, CE's sanitising cases (including ../../escape.txt, /etc/passwd, .env and ..), that path traversal stays inside vault/raw/, the size cap, non-multipart and file-less requests, ingest=false, ingest=true with CE present (draining through local ingest), with CE absent and a provider ready (agent runs), and with no backend (message, no runs). frontend/src/lib/uploadVault.test.ts covers the dialog's request (ingest flag first, one file field per file), the stored checkbox preference, and the result messages. embedMount.test.ts checks that the path is reserved.