Add README and cross-platform export tool

README documents minimal setup, run, and config for Linux and Windows. export.py bundles just the source into a zip (no .venv, caches, or API key files) for moving to another machine; it's pure stdlib run via 'uv run export.py', so it behaves identically on Linux and Windows with no shell required.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

export.py

@@ -0,0 +1,63 @@
+"""Bundle Blurt's source into a portable zip — e.g. to move it to another
+machine — leaving out the 200 MB+ .venv, caches, logs, and API key files.
+
+Cross-platform and dependency-free (stdlib only, no shell, no git), so it runs
+the same way on Linux and Windows:
+
+    uv run export.py [output.zip]      # default: <tempdir>/blurt-export.zip
+
+It only reads, never modifying this directory, so it is safe to run while Blurt
+is recording. On the other machine: unzip, then `uv sync` to rebuild .venv for
+that OS.
+"""
+
+import os
+import sys
+import tempfile
+import zipfile
+from pathlib import Path
+
+PROJECT_DIR = Path(__file__).resolve().parent
+ARCHIVE_ROOT = "blurt"  # top-level folder inside the zip
+
+# Never worth copying. API key files are excluded by name so secrets are never
+# swept in, even though they sit right next to the source.
+EXCLUDE_DIRS = {
+    ".git", ".venv", "__pycache__", ".claude",
+    "dist", "build", ".ruff_cache", ".pytest_cache",
+}
+EXCLUDE_NAMES = {"api_key.txt", "openrouter_key.txt"}
+EXCLUDE_SUFFIXES = {".pyc", ".pyo"}
+
+
+def _included_files():
+    for root, dirs, files in os.walk(PROJECT_DIR):
+        dirs[:] = [
+            d for d in dirs
+            if d not in EXCLUDE_DIRS and not d.endswith(".egg-info")
+        ]
+        for name in files:
+            if name in EXCLUDE_NAMES or Path(name).suffix in EXCLUDE_SUFFIXES:
+                continue
+            yield Path(root) / name
+
+
+def main():
+    default_out = Path(tempfile.gettempdir()) / "blurt-export.zip"
+    out = (Path(sys.argv[1]) if len(sys.argv) > 1 else default_out).resolve()
+    out.parent.mkdir(parents=True, exist_ok=True)
+
+    count = 0
+    with zipfile.ZipFile(out, "w", zipfile.ZIP_DEFLATED) as zf:
+        for path in _included_files():
+            if path.resolve() == out:  # don't zip the output into itself
+                continue
+            arcname = Path(ARCHIVE_ROOT) / path.relative_to(PROJECT_DIR)
+            zf.write(path, arcname)
+            count += 1
+
+    print(f"Wrote {out} ({count} files, {out.stat().st_size // 1024} KB)")
+
+
+if __name__ == "__main__":
+    main()