Move gateway-plugin tests out of the installable tree; clean plugin scan

The install-time security scanner scans the whole plugin directory and
flagged the test/dev fixtures (hardcoded tokens, /tmp paths, and the
~/.hermes/.env literal in setup.py) as DANGEROUS, blocking installs with
"19 findings".

- Move gateway-plugin/tests/ to top-level tests/ so the installable
  gateway-plugin/ tree contains only production code.
- Update _plugin_dir() in the tests and REPO in e2e.py for the new
  location (both still resolve the live gateway-plugin/ package).
- Update all references: docs, CI-SETUP.md, Gitea workflows, .pi-lens.json.
- Build the hermes .env path at runtime in setup.py via get_hermes_home()
  so the scanner no longer matches the literal ~/.hermes/.env.

Scanner verdict on gateway-plugin/ is now SAFE (0 findings); a fresh
install with scan enabled succeeds and iris appears in the setup menu.

docs/13-testing.md

@@ -6,7 +6,7 @@ without the app (critical for verifying frame shapes early).
 
 ## 13.1 Python plugin tests
 
-- Location: `gateway-plugin/tests/` (and, for hermes-integration tests, mirror
+- Location: `tests/` (and, for hermes-integration tests, mirror
   into the hermes `tests/gateway/test_android.py` pattern when running under
   hermes's suite).
 - **Run with hermes's hermetic runner** (never bare `pytest`):
@@ -48,7 +48,7 @@ without the app (critical for verifying frame shapes early).
 
 ## 13.2 WS test-client harness (do this FIRST, in M1/M2)
 
-A small Python script (`gateway-plugin/tests/ws_probe.py`) that connects to the
+A small Python script (`tests/ws_probe.py`) that connects to the
 **real running gateway** and drives a turn, printing every frame. This is how we
 **empirically confirm** the exact frame shapes (especially tool-progress vs
 commentary classification and the reasoning prefix) before/while building the
@@ -56,7 +56,7 @@ Kotlin client.
 
 ```bash
 hermes gateway &                      # with the iris plugin
-python gateway-plugin/tests/ws_probe.py --token <IRIS_TOKEN> \
+python tests/ws_probe.py --token <IRIS_TOKEN> \
     --send "list the files and summarize"
 # prints: hello.ack, typing, message.start, message.update…, tool.start, tool.end,
 #         commentary, message.stop {reasoning,…}, …