feat(client): T-1132 standalone Atlas companion shell + make atlas (D-254 SS3)

New atlas_standalone scene/script: attach-or-spawn boot (one REAL
connect_to_sim attempt at SR_PORT-or-9876 — a separate throwaway TCP
probe was proven by live run to kill a pre-accept-loop server via
broken handshake pipe; never abandon a connected socket), else spawn
--port 0 via new ServerProcess.start_with_pipe + LISTENING:{port}
stdout parse, retry against the resolved port. Reader role wired end
to end: protocol.encode_startup_message optional role param (empty
omits the wire key — byte-identical for all existing callers),
sim_bridge.connection_role suppresses the post-handshake
RequestAllSettings auto-send, hud_groups skips AutoPause/AutoResume
sends for readers (all three would otherwise burn Reader violation
strikes per the T-1130 matrix — endorsed by Oscar).

Generic implant host per D-254 SS3: the shell instantiates ALL
registered implant apps; implant_app_manifest gains
available_in_companion (opt-out, default true) and
implant_registry.instantiate_all a standalone filter param (default
preserves hud.gd behavior byte-identically). Boot order is
instantiate_all THEN open_app (reverse renders a permanently black
window — app_changed fires with no listener; matches hud.gd's order).
Owned-server lifecycle: _exit_tree stops a spawned child, attached
servers survive companion close. Known engine limitation documented:
raw SIGTERM bypasses all Godot notifications and orphans a spawned
server; WM close paths verified clean.

Live-verified: spawn-mode (301 systems rendered from systems.db over
the wire), attach-mode, two simultaneous readers, clean shutdown with
zero orphan processes. 14 new gdUnit tests (port/LISTENING parsing).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Makefile

@@ -1,6 +1,6 @@
 GODOT := $(shell command -v godot4 2>/dev/null || command -v godot 2>/dev/null)
 
-.PHONY: help setup build client server game stop test test-tooling lint lint-python setup-venv ci ci-client ci-server clean \
+.PHONY: help setup build client server game atlas stop test test-tooling lint lint-python setup-venv ci ci-client ci-server clean \
        decisions-sync decisions-active decisions-validate \
        validate-content check-fact-ids setup-hooks install-hooks \
        audit deny atlas-verify economy-db regen-db check-systems-db \
@@ -26,6 +26,7 @@ help:
 	@echo "  make setup-venv     Create .venv and install Python tooling deps"
 	@echo "  make build          Build client and server"
 	@echo "  make game           Build and run the full game (server + client)"
+	@echo "  make atlas          Standalone Atlas companion app — attach or spawn, read-only (D-254)"
 	@echo "  make stop           Stop any running server instance"
 	@echo "  make client         Run the Godot client (test mode)"
 	@echo "  make server         Run the Rust simulation server"
@@ -150,6 +151,20 @@ game: stop build
 	@SR_LIVE=1 $(GODOT) --path client
 	@$(MAKE) stop
 
+# D-254/T-1132: standalone Atlas companion app. Unlike `game`, no orchestration
+# here — atlas_standalone.gd owns its own attach-or-spawn decision and child
+# server lifecycle internally (D-254 §1/§3), so this target is just "build,
+# then launch the standalone scene". build-server ensures the debug binary
+# exists for spawn-mode (atlas_standalone.gd resolves it at
+# server/target/debug/settled-reach-server, the same path the E2E test files
+# use); build-client ensures imports are current. SR_LIVE=1 is required —
+# without it SimBridge boots in test mode (instant fake CONNECTED, no network
+# at all), which would make the companion open the Atlas against a dynamic
+# test-harness snapshot instead of the real systems.db world via the wire.
+atlas: build-server build-client
+	@test -n "$(GODOT)" || { echo "Godot not found. Run 'make setup' first."; exit 1; }
+	@SR_LIVE=1 $(GODOT) --path client scenes/atlas_standalone.tscn
+
 stop:
 	@lsof -ti :9876 | xargs -r kill 2>/dev/null || true
 	@echo "Stopped any running server on port 9876"