Add GUI-managed fake TCP clients

Introduce GUI test tooling that spawns synthetic TCP clients for local relay testing. Adds server/fake_player.py implementing FakePlayerClient and FakePlayerManager which create TCP connections to 127.0.0.1:7777, parse newline-delimited JSON, receive server-assigned playerId, and send one idle transform per second for cell 0B000F99. Integrates the manager into server/dev_server_app.py: start/stop lifecycle handling, Add/Remove buttons, table snapshots, logging bridge, and clean shutdown of fake clients. Updates server/README.md and docs/dev-log.md with usage, testing notes, and known issues. Includes basic error handling and thread-safe snapshots; movement scripts beyond Idle and full in-game validation are noted as next steps.

docs/dev-log.md

@@ -978,6 +978,66 @@ Player position: X=2048.00, Y=2048.00, Z=0.00, AngleZ=0.00
 
 ---
 
+## 2026-06-02 - GUI Fake Client Manager
+
+### Summary
+
+Added GUI-managed synthetic TCP clients for local relay testing. Fake clients
+connect through the normal server socket, receive a welcome `playerId`, send one
+idle transform per second for `F4TTestCell01`, and disconnect cleanly from the
+Fake Clients tab or when the GUI server stops.
+
+### Files Changed
+
+- `server/fake_player.py`
+- `server/dev_server_app.py`
+- `server/README.md`
+- `docs/dev-log.md`
+
+### Details
+
+- Added `FakePlayerClient` and `FakePlayerManager` as GUI test tooling only.
+- Fake clients use TCP `127.0.0.1:7777` and newline-separated JSON packets, so
+  the server sees them as normal external clients.
+- The Fake Clients tab now supports `+ Add Fake Client` and
+  `- Remove Selected`.
+- Fake-client lifecycle logs are routed to the GUI console with a
+  `[FakeClient]` prefix through the Qt signal bridge.
+- Stopping or closing the GUI disconnects all fake clients before stopping the
+  server.
+- The Fallout 4 plugin, network protocol, terminal server launcher, and
+  standalone `fake_client.py` were left unchanged.
+
+### Testing
+
+- Ran `python -m py_compile server.py server_core.py client_session.py
+  fake_client.py dev_server_app.py fake_player.py` from `server`; it succeeded.
+- Ran `python server.py` from `server` and confirmed the terminal launcher
+  reached the expected listening state.
+- Ran a headless fake-client smoke test on an alternate local port after
+  `127.0.0.1:7777` was temporarily held by another process. The fake client
+  received `playerId` 1, reached `Connected`, and the server recorded the idle
+  transform for `0B000F99`.
+- Imported `dev_server_app.py` successfully to confirm the GUI module and
+  PySide6 dependency load in the current Python environment.
+- Not yet run: interactive `python dev_server_app.py` GUI clicks.
+- Not yet run: Fallout 4/F4SE validation that a real client receives the fake
+  client's idle transform in `F4TTestCell01`.
+
+### Known Issues
+
+- No movement scripts beyond `Idle` are implemented yet.
+- Full Fallout 4/F4SE validation still needs to be run manually.
+
+### Next Steps
+
+- Add selectable fake-client movement scripts after the idle-client milestone is
+  validated.
+- Consider fake-client controls for script start/stop once multiple scripts
+  exist.
+
+---
+
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