Bump to v2.3.0: replace polling with SSE stream, fix detector imports

- Add GET /stream SSE endpoint to aggregator.py; state is pushed
  instantly on every change instead of fetched every 2s
- Replace setInterval polling in index.html with EventSource;
  onerror shows the ( ?.?) face and auto-reconnect is handled by
  the browser natively
- Fix ModuleNotFoundError in detectors: inject project root into
  PYTHONPATH when launching subprocesses from kao.py
- Update openapi.yaml, CLAUDE.md, README.md with /stream endpoint
- Remove completed SSE item from TODO.md

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

openapi.yaml

@@ -14,7 +14,7 @@ info:
     ## TTL/Heartbeat Pattern
     Events can have a TTL (time-to-live) that auto-expires them. Detectors typically send
     heartbeat events that expire if not refreshed, indicating loss of communication.
-  version: 2.2.0
+  version: 2.3.0
   license:
     name: MIT
 
@@ -183,12 +183,41 @@ paths:
               schema:
                 $ref: "#/components/schemas/WakeResponse"
 
+  /stream:
+    get:
+      summary: SSE stream of state updates
+      description: |
+        Server-Sent Events stream that pushes the current state as JSON whenever
+        it changes. The frontend connects here instead of polling `/status`.
+
+        Each event is a `data:` line containing a JSON-encoded Status object,
+        followed by a blank line. A `: keepalive` comment is sent every 30
+        seconds to prevent proxy timeouts. The current state is pushed
+        immediately on connection.
+
+        The browser's `EventSource` API handles automatic reconnection if the
+        connection drops.
+      operationId: getStream
+      responses:
+        "200":
+          description: Event stream
+          content:
+            text/event-stream:
+              schema:
+                type: string
+                description: |
+                  Newline-delimited SSE events. `data:` lines contain a
+                  JSON-encoded Status object. Lines beginning with `:` are
+                  keepalive comments and can be ignored.
+                example: "data: {\"current_state\": \"optimal\", ...}\n\n"
+
   /status:
     get:
       summary: Get current status
       description: |
         Returns the current display state including the active emote, color,
-        animation, and list of active events. The frontend polls this endpoint.
+        animation, and list of active events. Prefer `/stream` for live
+        displays; use this endpoint for one-shot queries.
       operationId: getStatus
       responses:
         "200":