feat: ability to use postgres as store for starter distro (#4076)

## What does this PR do?

The starter distribution now comes with all the required packages to
support persistent stores—like the agent store, metadata, and
inference—using PostgreSQL. Users can enable PostgreSQL support by
setting the `ENABLE_POSTGRES_STORE=1` environment variable.

This PR consolidates the functionality from the removed `postgres-demo`
distribution into the starter distribution, reducing maintenance
overhead.

**Closes: #2619**  
**Supersedes: #2851** (rebased and updated)

## Changes Made

1. **Added PostgreSQL support to starter distribution**
   - New `run-with-postgres-store.yaml` configuration
- Automatic config switching via `ENABLE_POSTGRES_STORE` environment
variable
   - Removed separate `postgres-demo` distribution

2. **Updated to new build system**
   - Integrated postgres switching logic into Containerfile entrypoint
   - Uses new `storage_backends` and `storage_stores` API
   - Properly configured both PostgreSQL KV store and SQL store

3. **Updated dependencies**
   - Added `psycopg2-binary` and `asyncpg` to starter distribution
   - All postgres-related dependencies automatically included

## How to Use

### With Docker (PostgreSQL):
```bash
docker run \
  -e ENABLE_POSTGRES_STORE=1 \
  -e POSTGRES_HOST=your_postgres_host \
  -e POSTGRES_PORT=5432 \
  -e POSTGRES_DB=llamastack \
  -e POSTGRES_USER=llamastack \
  -e POSTGRES_PASSWORD=llamastack \
  -e OPENAI_API_KEY=your_key \
  llamastack/distribution-starter
```

### PostgreSQL environment variables:
- `POSTGRES_HOST`: Postgres host (default: `localhost`)
- `POSTGRES_PORT`: Postgres port (default: `5432`)
- `POSTGRES_DB`: Postgres database name (default: `llamastack`)
- `POSTGRES_USER`: Postgres username (default: `llamastack`)
- `POSTGRES_PASSWORD`: Postgres password (default: `llamastack`)

## Test Plan

All pre-commit hooks pass (mypy, ruff, distro-codegen)  
`llama stack list-deps starter` confirms psycopg2-binary is included  
Storage configuration correctly uses PostgreSQL backends  
Container builds successfully with postgres support  

## Credits

Original work by @leseb in #2851. Rebased and updated by @r-bit-rry to
work with latest main.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Sébastien Han @leseb

---------

Signed-off-by: Sébastien Han <seb@redhat.com>
Co-authored-by: Sébastien Han <seb@redhat.com>

src/llama_stack/core/utils/config_resolution.py

@@ -52,7 +52,17 @@ def resolve_config_or_distro(
             logger.debug(f"Using distribution: {distro_config}")
             return distro_config
 
-    # Strategy 3: Try as built distribution name
+    # Strategy 3: Try as distro config path (if no .yaml extension and contains a slash)
+    # eg: starter::run-with-postgres-store.yaml
+    # Use :: to avoid slash and confusion with a filesystem path
+    if "::" in config_or_distro:
+        distro_name, config_name = config_or_distro.split("::")
+        distro_config = _get_distro_config_path(distro_name, config_name)
+        if distro_config.exists():
+            logger.info(f"Using distribution: {distro_config}")
+            return distro_config
+
+    # Strategy 4: Try as built distribution name
     distrib_config = DISTRIBS_BASE_DIR / f"llamastack-{config_or_distro}" / f"{config_or_distro}-{mode}.yaml"
     if distrib_config.exists():
         logger.debug(f"Using built distribution: {distrib_config}")
@@ -63,13 +73,15 @@ def resolve_config_or_distro(
         logger.debug(f"Using built distribution: {distrib_config}")
         return distrib_config
 
-    # Strategy 4: Failed - provide helpful error
+    # Strategy 5: Failed - provide helpful error
     raise ValueError(_format_resolution_error(config_or_distro, mode))
 
 
-def _get_distro_config_path(distro_name: str, mode: Mode) -> Path:
+def _get_distro_config_path(distro_name: str, mode: str) -> Path:
     """Get the config file path for a distro."""
-    return DISTRO_DIR / distro_name / f"{mode}.yaml"
+    if not mode.endswith(".yaml"):
+        mode = f"{mode}.yaml"
+    return DISTRO_DIR / distro_name / mode
 
 
 def _format_resolution_error(config_or_distro: str, mode: Mode) -> str:

src/llama_stack/core/utils/exec.py

@@ -84,6 +84,15 @@ def run_command(command: list[str]) -> int:
             text=True,
             check=False,
         )
+
+        # Print stdout and stderr if command failed
+        if result.returncode != 0:
+            log.error(f"Command {' '.join(command)} failed with returncode {result.returncode}")
+            if result.stdout:
+                log.error(f"STDOUT: {result.stdout}")
+            if result.stderr:
+                log.error(f"STDERR: {result.stderr}")
+
         return result.returncode
     except subprocess.SubprocessError as e:
         log.error(f"Subprocess error: {e}")