chore: bootstrap repository with governance docs

Initialize git, add Apache-2.0 LICENSE, .gitattributes (LF line
endings), AGENTS.md (entry points, stack, discovery order, baseline
checks), RUNBOOK.md (dev boot, prod deploy with overlay, ingestion,
failures, rollback, scaling notes), .env.prod.example with rotated
credential placeholders, and dev-only warnings on .env.example.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/utils/hashing.py

@@ -0,0 +1,21 @@
+"""Streaming SHA256 hashing utilities for large files."""
+
+from __future__ import annotations
+
+import hashlib
+from pathlib import Path
+
+_CHUNK = 1024 * 1024  # 1 MiB
+
+
+def sha256_file(path: Path | str) -> str:
+    """Compute SHA256 of a file in streaming mode (constant memory)."""
+    h = hashlib.sha256()
+    with open(path, "rb") as f:
+        for block in iter(lambda: f.read(_CHUNK), b""):
+            h.update(block)
+    return h.hexdigest()
+
+
+def sha256_bytes(data: bytes) -> str:
+    return hashlib.sha256(data).hexdigest()