src layout: move core code into src/tinyweb/ package

- Moved app.py, db.py, gateway.py, templates.py, embeddings.py,
  rns_client.py, and handlers/ into src/tinyweb/
- Created root app.py shim (adds src/ to sys.path, imports main)
- Created pyproject.toml with setuptools config (where = ["src"])
- Added src/tinyweb/__init__.py
- Updated all internal imports to use tinyweb. prefix (73 occurrences)
- Removed sys.path.insert hack from conftest.py
- Updated Dockerfile: pip install -e /app before running
- Updated gateway.py usage message: python -m tinyweb.gateway
- Updated README.md gateway usage instructions

tests/test_regressions.py

@@ -14,12 +14,12 @@ from unittest.mock import patch
 
 import pytest
 
-import app as app_module
-import db as db_module
-import handlers as handlers_module
+from tinyweb import app as app_module
+import tinyweb.db as db_module
+import tinyweb.handlers as handlers_module
 from conftest import patch_dns_fail, patch_dns_ok
-from db import clean_url
-from handlers import _sanitize_fts_query, handle_bulk_action
+from tinyweb.db import clean_url
+from tinyweb.handlers import _sanitize_fts_query, handle_bulk_action
 
 
 def test_6ffd38d_clean_url_preserves_www_when_bare_domain_fails(monkeypatch):
@@ -47,7 +47,7 @@ def test_1bc695f_fts_sanitizer_drops_operator_words(op):
 def test_1bc695f_gateway_rejects_oversize_body():
     """1bc695f: 16 MiB body-size cap prevents memory-exhaustion DoS."""
     from tests.test_gateway_limits import FakeGatewayHandler
-    from gateway import MAX_BODY_SIZE
+    from tinyweb.gateway import MAX_BODY_SIZE
     h = FakeGatewayHandler(
         path="/add", method="POST",
         headers={"Content-Length": str(MAX_BODY_SIZE + 1)},
@@ -70,7 +70,7 @@ def test_1bc695f_mesh_rejects_non_whitelisted_paths():
 def test_1bc695f_pool_returns_clean_connection(temp_db, monkeypatch):
     """1bc695f: uncommitted transactions on a pooled connection used to leak
     into the next consumer."""
-    from db import get_db, return_db
+    from tinyweb.db import get_db, return_db
     db = get_db()
     db.execute(
         "INSERT INTO pages (url, title, body) VALUES (?, ?, ?)",
@@ -88,7 +88,7 @@ def test_1bc695f_pool_returns_clean_connection(temp_db, monkeypatch):
 def test_8dffd8c_bulk_delete_requires_confirmation(seeded_db, csrf_session):
     """8dffd8c: bulk delete without confirmed=1 must render a confirm page
     instead of deleting — the JS confirm on /pages is a first-line filter only."""
-    from db import get_db, return_db
+    from tinyweb.db import get_db, return_db
     db = get_db()
     try:
         pid = db.execute("SELECT id FROM pages LIMIT 1").fetchone()["id"]