docs: add FLE bridge direction pivot and squad-injection test tooling

Adds the app-centric FLE bridge direction (direction.md) replacing the
Blaze-backend route as primary plan, plus a corrected foundational test
procedure and snapshot/diff/apply tooling for reverse-engineering FLE's
Freeze Lineup write mechanism. Also picks up prior untracked research docs
(status-review, fut-integration-options, fifa23-startup-flow, track-c) and
existing capture/export tooling that hadn't been committed yet.

tools/squad-injector/diff_snapshots.py

@@ -0,0 +1,77 @@
+#!/usr/bin/env python3
+"""Diff two openfut_snapshot_*.json files from snapshot_lineup_tables.lua.
+
+Usage: diff_snapshots.py before.json after.json
+
+Reports, per table, which rows changed and which fields differed —
+this is how the real DB write behind FLE's "Freeze Lineup" GUI feature
+gets discovered (see docs/foundational-xi-injection-test.md).
+"""
+import json
+import sys
+
+
+def row_key(row):
+    for candidate in ("playerid", "player_id", "id", "rowid"):
+        if candidate in row:
+            return row[candidate]
+    return json.dumps(row, sort_keys=True)
+
+
+def diff_table(name, before, after):
+    before_rows = {row_key(r): r for r in before.get("rows", [])}
+    after_rows = {row_key(r): r for r in after.get("rows", [])}
+
+    changes = []
+    for key, after_row in after_rows.items():
+        before_row = before_rows.get(key)
+        if before_row is None:
+            changes.append({"row": key, "type": "added", "row_data": after_row})
+            continue
+        field_diffs = {}
+        for field in set(before_row) | set(after_row):
+            bval = before_row.get(field)
+            aval = after_row.get(field)
+            if bval != aval:
+                field_diffs[field] = {"before": bval, "after": aval}
+        if field_diffs:
+            changes.append({"row": key, "type": "modified", "fields": field_diffs})
+
+    for key in before_rows:
+        if key not in after_rows:
+            changes.append({"row": key, "type": "removed"})
+
+    if changes:
+        print(f"\n=== {name}: {len(changes)} changed row(s) ===")
+        for c in changes:
+            print(json.dumps(c, indent=2))
+
+
+def main():
+    if len(sys.argv) != 3:
+        print(__doc__)
+        sys.exit(1)
+
+    with open(sys.argv[1]) as f:
+        before = json.load(f)
+    with open(sys.argv[2]) as f:
+        after = json.load(f)
+
+    table_names = set(before.get("tables", {})) | set(after.get("tables", {}))
+    any_changes = False
+    for name in sorted(table_names):
+        b = before.get("tables", {}).get(name, {"rows": []})
+        a = after.get("tables", {}).get(name, {"rows": []})
+        before_len = len(b.get("rows", []))
+        after_len = len(a.get("rows", []))
+        if before_len != after_len:
+            print(f"{name}: row count changed {before_len} -> {after_len}")
+            any_changes = True
+        diff_table(name, b, a)
+
+    if not any_changes:
+        print("(row-count-only check found no differences; per-field diffs above are authoritative)")
+
+
+if __name__ == "__main__":
+    main()