Pre-install server deps for fast devcontainer start. Fix dev launch.json

There seems to be a more standard mechanism of specifying launch.json
params for devcontainers. Previous mechanism to write launch.json to
.vscode/launch.json in post creation step does not work.

Improve default launch.json to include khoj admin username, password
with placeholder values to get started with local development faster.

Define dockerfile for devcontainer to pre-built server, web app
dependencies during dev container image creation stage. So install on
dev container startup is sped up as no need to install dependencies.

.devcontainer/Dockerfile

@@ -0,0 +1,36 @@
+ARG PYTHON_VERSION=3.10
+FROM mcr.microsoft.com/devcontainers/python:${PYTHON_VERSION}
+
+WORKDIR /workspace
+
+# --- Python Server App Dependencies ---
+# Create Python virtual environment
+RUN python3 -m venv .venv
+# Add venv to PATH for subsequent RUN commands and for the container environment
+ENV PATH="/workspace/.venv/bin:${PATH}"
+
+# Copy files required for Python dependency installation.
+COPY pyproject.toml README.md ./
+
+# Setup python environment
+    # Use the pre-built llama-cpp-python, torch cpu wheel
+ENV PIP_EXTRA_INDEX_URL="https://download.pytorch.org/whl/cpu https://abetlen.github.io/llama-cpp-python/whl/cpu" \
+    # Avoid downloading unused cuda specific python packages
+    CUDA_VISIBLE_DEVICES="" \
+    # Use static version to build app without git dependency
+    VERSION=0.0.0
+# Install Python dependencies from pyproject.toml in editable mode
+RUN sed -i "s/dynamic = \\[\"version\"\\]/version = \"$VERSION\"/" pyproject.toml && \
+    pip install --no-cache-dir ".[dev]"
+
+# --- Web App Dependencies ---
+# Copy web app manifest files
+COPY src/interface/web/package.json src/interface/web/yarn.lock ./src/interface/web/
+
+# Install web app dependencies
+# note: node and yarn will be available from the "features" in devcontainer.json
+RUN yarn install --cwd ./src/interface/web && yarn export --cwd ./src/interface/web
+
+# The .venv and node_modules are now populated in the image.
+# The rest of the source code will be mounted by VS Code from your local checkout,
+# overlaying any files copied here if they are part of the workspace mount.

.devcontainer/devcontainer.json

@@ -1,6 +1,12 @@
 {
     "name": "Khoj Development Environment",
-    "image": "mcr.microsoft.com/devcontainers/python:3.10",
+    "build": {
+        "dockerfile": "Dockerfile",
+        "context": "..", // Build context is the project root
+        "args": {
+            "PYTHON_VERSION": "3.10"
+        }
+    },
     "forwardPorts": [
         42110
     ],
@@ -40,11 +46,39 @@
                     "tests"
                 ],
                 "python.testing.unittestEnabled": false,
-                "python.testing.pytestEnabled": true
+                "python.testing.pytestEnabled": true,
+                "launch": {
+                    "configurations": [
+                        {
+                            "name": "Launch Khoj",
+                            "type": "debugpy",
+                            "request": "launch",
+                            "module": "src.khoj.main",
+                            "console": "integratedTerminal",
+                            "justMyCode": false,
+                            "sudo": true,
+                            "args": [
+                                "-v",
+                                "--anonymous-mode",
+                                "--non-interactive",
+                                "--port=42110"
+                            ],
+                            "envFile": "${workspaceFolder}/.env",
+                            "env": {
+                                "KHOJ_ADMIN_EMAIL": "admin",
+                                "KHOJ_ADMIN_PASSWORD": "admin",
+                                "USE_EMBEDDED_DB": "true",
+                                "KHOJ_DEBUG": "true",
+                                "KHOJ_TELEMETRY_DISABLED": "true",
+                                "PROMPTRACE_DIR": "${workspaceFolder}/promptrace"
+                            }
+                        }
+                    ]
+                }
             }
         }
     },
-    "postCreateCommand": "scripts/dev_setup.sh --devcontainer",
+    "postCreateCommand": "scripts/dev_setup.sh",
     "features": {
         "ghcr.io/devcontainers-contrib/features/black:2": {},
         "ghcr.io/devcontainers-contrib/features/mypy:2": {},