feat(sources): upload tarball/zipfile archives as sources — unpack, scan, and replace in place

Phase 49 (owner request, chat 2026-08-28: "The git sources page should
remove local directory and should instead accept a tarball or zipfile
upload which it will unpack and scan … reuploading the same tarball
should not create a new folder, but should unpack and overwrite the
previously unpacked content" — design confirmed in the same
conversation):

* POST /api/git-sources/upload (admin-only, require_admin): accepts
  .tar/.tar.gz/.tgz/.zip, streams it with the BOR_UPLOAD_MAX_MB cap
  (bounds BOTH the compressed upload and the total extracted bytes —
  zip-bomb guard), safely unpacks (absolute/traversal/symlink/hardlink
  escape and device/FIFO members rejected), and atomically swaps the
  content in over BOR_UPLOAD_DIR/<name>/ (name = filename minus the
  archive suffix — no missing window, a failed upload never touches the
  existing folder/row/KB). The git_sources row is upserted by path
  (kind='local', no duplicates, added_at preserved), the models are
  checked fail-fast (503 sanitized when down — the folder/row stay
  committed and the next sync/re-upload retries idempotently), and the
  source is scanned synchronously in the request (single-source
  import_sources prune=True + change-gated KB overview), answering 200
  with the sync-style counts. One upload at a time (409); the request
  session is released before the scan so a concurrent TRUNCATE cannot
  deadlock against it.
* app/rag/archive_upload.py: ArchiveUploadError, ARCHIVE_SUFFIXES,
  archive_source_name (safe-name derivation), unpack_archive (guarded
  zip/tar extraction with the extracted-byte cap, no partial state),
  swap_in (atomic replace with restore-on-failure) — fully unit-tested.
* app/config.py + .env.example: BOR_UPLOAD_DIR (default
  ~/bor-sources/uploads, deliberately separate from the git checkouts)
  and BOR_UPLOAD_MAX_MB (default 512; a validator fails loud at
  startup on <= 0).
* python-multipart added to the dependencies — FastAPI's required
  multipart parser (an A2 implementation detail, phase locked decision).
* The Sources page: the phase-38 "Add a local directory" form is
  removed; #archive-upload-form takes its place (labeled file input,
  "Upload & scan" button, the §7.4 never-stale lifecycle, inline
  role=alert error, role=status count line); hint + table caption
  updated. The POST /api/git-sources kind=local API contract is
  UNCHANGED — a plain directory is still registrable via the API, and
  existing Local rows list/remove/sync exactly as before.
* The phase-38 story E2E (test_local_directory_sources.py) is rewritten
  API-driven — the form it drove is gone; its acceptance stands.
* The story E2E (test_archive_upload_sources.py): the swap,
  upload→scan→list (the deterministic "Uploading…" in-flight state, the
  Local row, /api/docs + the RAG catalog), same-filename re-upload
  (in-place replace, prune, no duplicate row, v2-only folder), the
  422 inline error + recovery (the form is not wedged), and the
  anonymous gate + 403.
* README: the archive-upload section (formats, naming rule, in-place
  replace, both new settings), the local-directory form removal noted,
  config reference rows for BOR_UPLOAD_DIR / BOR_UPLOAD_MAX_MB.

Gates: unit+integration green, app/ coverage 99%, the story E2E green
in isolation, the regression suites (git sources admin, local
directory sources, sync button, import documents, nav rename, smoke,
shared header) green in isolation, ruff + pyright clean.

Note: per this phase's file-level staging, frontend/assets/styles.css
also carries the small same-day in-flight owner rework already in the
working tree (the .sign-in-mobile companion rule for the phase-48
mobile sign-in copy); the phase-49 change is the upload form's block.

.env.example

@@ -66,6 +66,17 @@ BOR_RRF_K=60                      # Reciprocal Rank Fusion damping constant
 # BOR_GIT_SOURCES=https://github.com/user/homelab.git,https://github.com/user/deployments.git
 # BOR_SOURCES_DIR=~/bor-sources
 
+# Phase 49: uploaded source archives (the Sources page upload form).
+# An uploaded .tar / .tar.gz / .tgz / .zip is unpacked to
+# BOR_UPLOAD_DIR/<name>/ where <name> is the filename minus the archive
+# suffix (homelab.tar.gz -> homelab/). Re-uploading the same name
+# replaces the folder's content IN PLACE — one folder, one row, no
+# missing window; a failed upload never touches the existing folder,
+# row, or KB. Deliberately separate from BOR_SOURCES_DIR (git checkouts).
+# BOR_UPLOAD_DIR=~/bor-sources/uploads
+# BOR_UPLOAD_MAX_MB=512   # caps BOTH the compressed upload and the total
+                          # extracted bytes (zip-bomb guard); must be > 0
+
 # --- Admin & sign-in (single-admin password login; BOTH required) ---
 # The app refuses to start while either is empty (names the missing
 # variable(s) — README "Admin & sign-in"). Generate the secret with: