feat(server): implement GET /api/health platform health/version route

Unauthenticated probe route per the addon-contract §4.8 interim spec
(work item W7): 200 {"status": "ok", "platform_version": "<release>"}.
platform_version is read from the root VERSION file (bumped to v0.5.0,
served without the v prefix); consumers are examonctl plan/qualify.
Both images bake VERSION in: the standalone image next to server.py,
the compose image at EXAMON_HOME so the dev bind-mount cannot hide it.

Author: fbeneventi

Dockerfile

@@ -7,6 +7,9 @@ ADD ./publishers/random_pub ${EXAMON_HOME}/publishers/random_pub
 ADD ./docker/examon/supervisor.conf /etc/supervisor/conf.d/supervisor.conf
 ADD ./scripts/examon.conf $EXAMON_HOME/scripts/examon.conf
 ADD ./web $EXAMON_HOME/web
+# Platform release version served by /api/health; kept at EXAMON_HOME so the
+# compose bind-mount of web/examon-server does not hide it
+ADD ./VERSION $EXAMON_HOME/VERSION
 
 # Venvs
 WORKDIR $EXAMON_HOME/scripts

VERSION

@@ -1 +1 @@
-v0.4.0
+v0.5.0

deploy/docker/examon-server/Dockerfile

@@ -10,6 +10,7 @@ COPY web/examon-server/requirements.txt .
 RUN CASS_DRIVER_BUILD_CONCURRENCY=8 pip install --no-cache-dir -r requirements.txt
 
 COPY web/examon-server/ .
+COPY VERSION .
 
 EXPOSE 5000
 

web/examon-server/server.py

@@ -250,6 +250,32 @@ def localize_timestamps(df, tz):
                 df[col] = df[col].dt.tz_convert(tz)
     return df
 
+def _read_platform_version():
+    """Read the platform release version from the root VERSION file.
+
+    Looks next to this file first (standalone image bakes it in /app),
+    then two levels up (repo root / legacy image EXAMON_HOME).
+    """
+    base_dir = os.path.dirname(os.path.abspath(__file__))
+    for candidate in (os.path.join(base_dir, 'VERSION'),
+                      os.path.abspath(os.path.join(base_dir, '..', '..', 'VERSION'))):
+        try:
+            with open(candidate) as f:
+                version = f.read().strip()
+                return version[1:] if version.startswith('v') else version
+        except (IOError, OSError):
+            continue
+    return 'unknown'
+
+
+PLATFORM_VERSION = _read_platform_version()
+
+
+@app.route('/api/health')
+def health():
+    return jsonify({'status': 'ok', 'platform_version': PLATFORM_VERSION}), 200
+
+
 @app.route('/')
 @auth.login_required
 def index():