feat: DuckDB two-file architecture — resolve SQLMesh/web-app lock contention

Split the single lakehouse.duckdb into two files to eliminate the exclusive
write-lock conflict between SQLMesh (pipeline) and the Quart web app (reader):

  lakehouse.duckdb  — SQLMesh exclusive (all pipeline layers)
  serving.duckdb    — web app reads (serving tables only, atomically swapped)

Changes:

web/src/beanflows/analytics.py
- Replace persistent global _conn with per-thread connections (threading.local)
- Add _get_conn(): opens read_only=True on first call per thread, reopens
  automatically on inode change (~1μs os.stat) to pick up atomic file swaps
- Switch env var from DUCKDB_PATH → SERVING_DUCKDB_PATH
- Add module docstring documenting architecture + DuckLake migration path

web/src/beanflows/app.py
- Startup check: use SERVING_DUCKDB_PATH
- Health check: use _db_path instead of _conn

src/materia/export_serving.py (new)
- Reads all serving.* tables from lakehouse.duckdb (read_only)
- Writes to serving_new.duckdb, then os.rename → serving.duckdb (atomic)
- ~50 lines; runs after each SQLMesh transform

src/materia/pipelines.py
- Add export_serving pipeline entry (uv run python -c ...)

infra/supervisor/supervisor.sh
- Add SERVING_DUCKDB_PATH env var comment
- Add export step: uv run materia pipeline run export_serving

infra/supervisor/materia-supervisor.service
- Add Environment=SERVING_DUCKDB_PATH=/data/materia/serving.duckdb

infra/bootstrap_supervisor.sh
- Add SERVING_DUCKDB_PATH to .env template

web/.env.example + web/docker-compose.yml
- Document both env vars; switch web service to SERVING_DUCKDB_PATH

web/src/beanflows/dashboard/templates/settings.html
- Minor settings page fix from prior session

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

infra/bootstrap_supervisor.sh

@@ -93,6 +93,7 @@ PULUMI_ACCESS_TOKEN=${PULUMI_ACCESS_TOKEN}
 PATH=/root/.cargo/bin:/root/.pulumi/bin:/usr/local/bin:/usr/bin:/bin
 LANDING_DIR=/data/materia/landing
 DUCKDB_PATH=/data/materia/lakehouse.duckdb
+SERVING_DUCKDB_PATH=/data/materia/serving.duckdb
 EOF
 
 echo "--- Setting up systemd service ---"

infra/supervisor/materia-supervisor.service

@@ -13,6 +13,7 @@ RestartSec=10
 EnvironmentFile=/opt/materia/.env
 Environment=LANDING_DIR=/data/materia/landing
 Environment=DUCKDB_PATH=/data/materia/lakehouse.duckdb
+Environment=SERVING_DUCKDB_PATH=/data/materia/serving.duckdb
 
 # Resource limits
 LimitNOFILE=65536

infra/supervisor/supervisor.sh

@@ -4,9 +4,10 @@
 # https://github.com/tigerbeetle/tigerbeetle/blob/main/src/scripts/cfo_supervisor.sh
 #
 # Environment variables (set in systemd EnvironmentFile):
-#   LANDING_DIR        — local path for extracted landing data
-#   DUCKDB_PATH        — path to DuckDB lakehouse file
-#   ALERT_WEBHOOK_URL  — optional ntfy.sh / Slack / Telegram webhook for failure alerts
+#   LANDING_DIR          — local path for extracted landing data
+#   DUCKDB_PATH          — path to DuckDB lakehouse file (SQLMesh pipeline DB)
+#   SERVING_DUCKDB_PATH  — path to serving-only DuckDB (web app reads from here)
+#   ALERT_WEBHOOK_URL    — optional ntfy.sh / Slack / Telegram webhook for failure alerts
 
 set -eu
 
@@ -51,6 +52,13 @@ do
         DUCKDB_PATH="${DUCKDB_PATH:-/data/materia/lakehouse.duckdb}" \
             uv run materia pipeline run transform
 
+        # Export serving tables to serving.duckdb (atomic swap).
+        # The web app reads from SERVING_DUCKDB_PATH and picks up the new file
+        # automatically via inode-based connection reopen — no restart needed.
+        DUCKDB_PATH="${DUCKDB_PATH:-/data/materia/lakehouse.duckdb}" \
+        SERVING_DUCKDB_PATH="${SERVING_DUCKDB_PATH:-/data/materia/serving.duckdb}" \
+            uv run materia pipeline run export_serving
+
     ) || {
         # Notify on failure if webhook is configured, then sleep to avoid busy-loop
         if [ -n "${ALERT_WEBHOOK_URL:-}" ]; then