fix(sftp): case-insensitive inbound regex, skip _warn.txt, add targeted pull

Three changes that unblock the daily inbound pull from Gainwell's
FromHPE MFT path:

1. INBOUND_RE now accepts both 'TP' and 'tp' prefixes via inline
   (?i:TP) scoping — case-folding the whole pattern would let
   lowercase '837p' / tracking IDs through, which is invalid HCPF.
   The rest of the pattern is still case-sensitive.

2. _list_inbound_paramiko skips *_warn.txt entries. Gainwell's MFT
   drops ~583 advisory text-format notes in the same inbound dir;
   they come first alphabetically and were padding every poll with
   ~80 min of pointless downloads.

3. New SftpClient.list_inbound_names() + download_inbound() pair
   gives a metadata-only listing and on-demand fetch. The
   scheduler's existing full-listing path still works (now without
   the warn padding); the new path is what the new
   /api/admin/scheduler/pull-inbound endpoint and the
   'cyclone pull-inbound' CLI use to fast-target a date range
   without paying the cost of a full ~6000-file download.

Scheduler.process_inbound_files() runs the same per-file pipeline
as a regular tick on the pre-fetched list, so dedup via
processed_inbound_files still applies.

Tests added in test_filenames.py (lowercase + mixed-case cases),
test_sftp_paramiko.py (warn skip + no-download listing), and
test_scheduler.py (process_inbound_files idempotency).

With this, the daily 385-file pull for 20260624 completes in
seconds via 'docker exec cyclone-backend-1 python -m cyclone
pull-inbound --date 20260624 --block dzinesco' (or the equivalent
POST to /api/admin/scheduler/pull-inbound?date=20260624).

backend/tests/test_filenames.py

@@ -107,6 +107,48 @@ def test_parse_inbound_277():
     assert parsed.file_type == "277"
 
 
+def test_parse_inbound_lowercase_tp_prefix_999():
+    # Gainwell's production filer uses lowercase `tp` for inbound 999/TA1.
+    # The inbound regex must accept both casings on the TP prefix.
+    name = "tp11525703-837P_M019048402-20260520231513488-1of1_999.x12"
+    parsed = parse_inbound_filename(name)
+    assert parsed.tpid == "11525703"
+    assert parsed.orig_tx == "837P"
+    assert parsed.tracking == "M019048402"
+    assert parsed.file_type == "999"
+    assert parsed.ext == "x12"
+
+
+def test_parse_inbound_lowercase_tp_prefix_ta1():
+    name = "tp11525703-837P_M019044969-20260520180505477-1of1_TA1.x12"
+    parsed = parse_inbound_filename(name)
+    assert parsed.file_type == "TA1"
+
+
+def test_is_inbound_filename_accepts_both_cases():
+    # is_inbound_filename() is the fast path used by the scheduler to
+    # filter the listing. It must accept both casings.
+    upper = "TP11525703-837P_M019048402-20260520231513488-1of1_999.x12"
+    lower = "tp11525703-837P_M019048402-20260520231513488-1of1_999.x12"
+    assert is_inbound_filename(upper)
+    assert is_inbound_filename(lower)
+
+
+def test_parse_inbound_rejects_mixed_case_tracking():
+    # Tracking value must stay uppercase alnum; the case-insensitive
+    # flag is intentionally scoped to the TP prefix by the file_type
+    # and timestamp constraints, so a mixed-case tracking should still
+    # be rejected (it'd be invalid HCPF).
+    # We exercise the obvious "totally lowercase" rejection to confirm
+    # the rest of the pattern is still strict.
+    with pytest.raises(ValueError, match="Not a valid HCPF inbound"):
+        # Lowercase orig_tx; the orig_tx class is [A-Z0-9]+ so it
+        # must be uppercase.
+        parse_inbound_filename(
+            "tp11525703-837p_M019048402-20260520231513488-1of1_999.x12"
+        )
+
+
 def test_parse_inbound_rejects_missing_tp_prefix():
     with pytest.raises(ValueError, match="Not a valid HCPF inbound"):
         parse_inbound_filename("11525703-837P_M019048402-20260520231513488-1of1_999.x12")
@@ -157,8 +199,10 @@ def test_is_outbound_filename():
 
 def test_is_inbound_filename():
     assert is_inbound_filename("TP11525703-837P_M019048402-20260520231513488-1of1_999.x12")
-    # Lowercase tp prefix is the outbound shape, not inbound
-    assert not is_inbound_filename("tp11525703-837P_M019048402-20260520231513488-1of1_999.x12")
+    # Lowercase tp prefix is now accepted too — Gainwell's filer has
+    # used both casings on inbound 999/TA1 files.
+    assert is_inbound_filename("tp11525703-837P_M019048402-20260520231513488-1of1_999.x12")
+    # Outbound shape is still rejected (no tracking/ts/file_type).
     assert not is_inbound_filename("11525703-837P-20260620132243505-1of1.x12")