feat: Claude Code Monitor — lanes, pipelines and a merged workspace

Internal SmartGift build of a Claude Code monitoring dashboard.

Lanes: a durable unit of parallel agent work, one per working directory,
tracked across session restarts. Managed lanes are git worktrees the
dashboard provisions and can reset or remove behind a three-check destroy
guard and a counted preflight; adopted lanes are directories you already
own and are never destroyable.

Pipelines: a lane moves through pipeline stages. A stage the agent declares
with evidence renders green; a stage inferred from the tool-event stream
renders dashed amber and never counts as done. Detection is forward-only
within a 30-minute window, and never writes the declared stage.

Workspace: one page at /run with a lane grid, the selected lane's pipeline,
and a full Claude console behind a disclosure.

.devcontainer/Dockerfile

@@ -0,0 +1,23 @@
+# Optional dev-container image for Claude Code Agent Monitor.
+# Node 22 to match the production Dockerfile and the project's engines.
+# Adds the native-addon toolchain (better-sqlite3 builds via node-gyp) plus
+# Python 3 (statusline.py and helper scripts) and the sqlite3 CLI.
+#
+# This image is ONLY used by Dev Containers / Codespaces. Host-based development
+# (npm run dev / npm start) is unaffected.
+#
+# Author: Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+FROM mcr.microsoft.com/devcontainers/javascript-node:22
+
+# node-gyp needs python3 + a C/C++ toolchain to compile better-sqlite3.
+# python-is-python3 makes `python` resolve to python3 for node-gyp.
+# sqlite3 is handy for inspecting the dashboard DB during development.
+RUN export DEBIAN_FRONTEND=noninteractive \
+  && apt-get update \
+  && apt-get install -y --no-install-recommends \
+  build-essential \
+  python3 \
+  python-is-python3 \
+  sqlite3 \
+  && apt-get clean \
+  && rm -rf /var/lib/apt/lists/*