chore: consolidate runtime data layout under single data/ root directory

Migrate all runtime artifacts (database, uploads, VAPID keys, locks, bot state, container workspaces, zip staging) from scattered locations (`var/`, `devplacepy/static/uploads/`) into a unified `data/` directory. Update `config.py` as single source of truth with `DATA_PATHS` registry and `ensure_data_dirs()`, add `devplace migrate-data` CLI command with CRC verification and idempotent relocation, adjust `.dockerignore`, `.env.example`, `.gitignore`, `Dockerfile`, `Makefile`, `README.md`, `AGENTS.md`, `CLAUDE.md`, and all import paths in `attachments.py` to reference `config.UPLOADS_DIR`/`ATTACHMENTS_DIR` instead of computing from `STATIC_DIR`.

devplacepy/attachments.py

@@ -11,7 +11,7 @@ from PIL import Image
 from io import BytesIO
 import httpx
 from devplacepy.database import get_table, db, get_setting
-from devplacepy.config import STATIC_DIR
+from devplacepy.config import UPLOADS_DIR, ATTACHMENTS_DIR
 from devplacepy.utils import generate_uid
 
 logger = logging.getLogger(__name__)
@@ -22,8 +22,6 @@ REMOTE_FETCH_USER_AGENT = (
     "(KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36"
 )
 
-UPLOADS_DIR = STATIC_DIR / "uploads"
-ATTACHMENTS_DIR = UPLOADS_DIR / "attachments"
 THUMBNAIL_SIZE = (200, 200)
 THUMBNAIL_QUALITY = 80
 IMAGE_EXTENSIONS = {".jpg", ".jpeg", ".png", ".gif", ".webp", ".bmp", ".tiff"}