Remove encryption; user-data filters; SQLite safety; recovery, retention, scheduler

- No client-side encryption: plaintext content-addressed remote (SHA-256
  names), no backup key, no cryptography dependency (server disk encryption
  is the trust model).
- Filters back user data: images, archives, databases, PDFs accepted; 10 MiB
  cap; binary sniffing removed; temp names hardened (~$, #..#, .temp).
- SQLite zero-error policy: backup-API snapshots + integrity_check, journal
  folding, locked/corrupt loud skips, verified restores.
- Recovery: reindex from manifests, remote adopt, on-demand blob fetch,
  5-day retention + thinning, GC, date-guarded remote purge, metrics.
- Scheduler with WebDAV quota signal and 70% pressure backstop (floor kept).
- 37 tests incl. live-monitor capture safety and DB safety.

tests/test_service.py

@@ -155,7 +155,7 @@ def test_push_snapshots_and_limits(env):
     assert client.post("/api/v1/snapshots", json=body).json()["status"] == "committed"
     assert client.post("/api/v1/snapshots", json=body).json()["status"] == "unchanged"
 
-    big = {**body, "content_b64": base64.b64encode(b"x" * 204_801).decode()}
+    big = {**body, "content_b64": base64.b64encode(b"x" * 10_485_761).decode()}
     r = client.post("/api/v1/snapshots", json=big)
     assert r.status_code == 413 and r.headers["content-type"] == "application/problem+json"