Fix 3 architectural bottlenecks blocking cross-domain adoption

Bottleneck 1: ImageHashes generalization
- phash and dhash now default to "" (optional), enabling attestation
  of CSV datasets, sensor logs, documents, and any non-image file
- Added ImageHashes.from_file() for arbitrary file attestation
  (SHA-256 only, no perceptual hashes)
- Added ImageHashes.is_image property to check if perceptual matching
  is meaningful
- Added content_type field to AttestationRecord ("image", "document",
  "data", "audio", "video") — backward compatible, defaults to "image"
- from_dict() now tolerates missing phash/dhash fields

Bottleneck 2: Lazy path resolution
- Converted 5 modules from eager top-level path imports to lazy
  access via `import soosef.paths as _paths`:
  config.py, deadman.py, usb_monitor.py, tamper.py, anchors.py
- Paths now resolve at use-time, not import-time, so --data-dir
  and SOOSEF_DATA_DIR overrides propagate correctly to all modules
- Enables portable mode (run entirely from USB stick)
- Updated deadman enforcement tests for new path access pattern

Bottleneck 3: Delivery acknowledgment chain records
- New CONTENT_TYPE_DELIVERY_ACK = "soosef/delivery-ack-v1"
- ChainStore.append_delivery_ack() records bundle receipt with
  sender fingerprint and record count
- import_attestation_bundle() auto-generates ack when chain store
  and private key are provided
- Enables two-way federation handshakes (art provenance, legal
  chain of custody, multi-org evidence exchange)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/test_deadman_enforcement.py

@@ -64,7 +64,7 @@ def test_enforcement_loop_no_op_when_disarmed(tmp_path: Path, monkeypatch: pytes
 
     # Redirect the module-level DEADMAN_STATE constant so DeadmanSwitch() default is our tmp file
     state_file = tmp_path / "deadman.json"
-    monkeypatch.setattr(deadman_mod, "DEADMAN_STATE", state_file)
+    monkeypatch.setattr(deadman_mod, "_paths", type("P", (), {"DEADMAN_STATE": state_file}))
 
     check_calls = []
 
@@ -94,7 +94,7 @@ def test_enforcement_loop_fires_when_overdue(tmp_path: Path, monkeypatch: pytest
     from soosef.fieldkit import deadman as deadman_mod
 
     state_file = tmp_path / "deadman.json"
-    monkeypatch.setattr(deadman_mod, "DEADMAN_STATE", state_file)
+    monkeypatch.setattr(deadman_mod, "_paths", type("P", (), {"DEADMAN_STATE": state_file}))
 
     last_checkin = datetime.now(UTC) - timedelta(hours=100)
     _write_deadman_state(
@@ -124,7 +124,7 @@ def test_enforcement_loop_exits_after_firing(tmp_path: Path, monkeypatch: pytest
     from soosef.fieldkit import deadman as deadman_mod
 
     state_file = tmp_path / "deadman.json"
-    monkeypatch.setattr(deadman_mod, "DEADMAN_STATE", state_file)
+    monkeypatch.setattr(deadman_mod, "_paths", type("P", (), {"DEADMAN_STATE": state_file}))
 
     last_checkin = datetime.now(UTC) - timedelta(hours=100)
     _write_deadman_state(state_file, armed=True, last_checkin=last_checkin)
@@ -149,7 +149,7 @@ def test_enforcement_loop_tolerates_exceptions(tmp_path: Path, monkeypatch: pyte
     from soosef.fieldkit import deadman as deadman_mod
 
     state_file = tmp_path / "deadman.json"
-    monkeypatch.setattr(deadman_mod, "DEADMAN_STATE", state_file)
+    monkeypatch.setattr(deadman_mod, "_paths", type("P", (), {"DEADMAN_STATE": state_file}))
 
     call_count = [0]
 
@@ -212,7 +212,7 @@ def test_check_deadman_disarmed(
 
     # Point at an empty tmp dir so the real ~/.soosef/fieldkit/deadman.json isn't read
     state_file = tmp_path / "deadman.json"
-    monkeypatch.setattr(deadman_mod, "DEADMAN_STATE", state_file)
+    monkeypatch.setattr(deadman_mod, "_paths", type("P", (), {"DEADMAN_STATE": state_file}))
 
     result = cli_runner.invoke(main, ["fieldkit", "check-deadman"])
     assert result.exit_code == 0
@@ -227,7 +227,7 @@ def test_check_deadman_armed_ok(
     from soosef.fieldkit import deadman as deadman_mod
 
     state_file = tmp_path / "deadman.json"
-    monkeypatch.setattr(deadman_mod, "DEADMAN_STATE", state_file)
+    monkeypatch.setattr(deadman_mod, "_paths", type("P", (), {"DEADMAN_STATE": state_file}))
 
     last_checkin = datetime.now(UTC) - timedelta(hours=1)
     _write_deadman_state(
@@ -251,7 +251,7 @@ def test_check_deadman_overdue_in_grace(
     from soosef.fieldkit import deadman as deadman_mod
 
     state_file = tmp_path / "deadman.json"
-    monkeypatch.setattr(deadman_mod, "DEADMAN_STATE", state_file)
+    monkeypatch.setattr(deadman_mod, "_paths", type("P", (), {"DEADMAN_STATE": state_file}))
 
     # Past 24h interval but within 26h total (grace=2)
     last_checkin = datetime.now(UTC) - timedelta(hours=25)
@@ -277,7 +277,7 @@ def test_check_deadman_fires_when_expired(
     from soosef.fieldkit import deadman as deadman_mod
 
     state_file = tmp_path / "deadman.json"
-    monkeypatch.setattr(deadman_mod, "DEADMAN_STATE", state_file)
+    monkeypatch.setattr(deadman_mod, "_paths", type("P", (), {"DEADMAN_STATE": state_file}))
 
     last_checkin = datetime.now(UTC) - timedelta(hours=100)
     _write_deadman_state(