feat: build system hardening — collision detection, validation gates, init path enforcement

5-phase hardening to prevent silent file-layer collisions (the D-Bus
regression class):

Phase 1: lint-config-paths.sh + make lint-config in depends.mk
Phase 2: CollisionTracker in installer (content-hash comparison)
Phase 3: installs manifests in recipe.toml + validate-file-ownership.sh
Phase 4: validate-init-services.sh + make validate in disk.mk
Phase 5: documentation (AGENTS.md, BUILD-SYSTEM-HARDENING-PLAN.md)

Both redbear-mini and redbear-full build and validate clean.
66 declared install paths in base, zero conflicts.

config/redbear-greeter-services.toml

@@ -3,7 +3,7 @@
 # This fragment is intended to be included by the active desktop/graphics target.
 
 [[files]]
-path = "/usr/lib/init.d/05_boot-essential.target"
+path = "/etc/init.d/05_boot-essential.target"
 data = """
 [unit]
 description = "Boot essential services target"
@@ -30,7 +30,7 @@ redbear-session-launch = {}
 redbear-greeter = {}
 
 [[files]]
-path = "/usr/lib/init.d/19_redbear-authd.service"
+path = "/etc/init.d/19_redbear-authd.service"
 data = """
 [unit]
 description = "Red Bear authentication daemon"
@@ -44,7 +44,7 @@ type = "oneshot_async"
 """
 
 [[files]]
-path = "/usr/lib/init.d/20_display.service"
+path = "/etc/init.d/20_display.service"
 data = """
 [unit]
 description = "Compositor proof (Phase 2: KWin virtual + Qt6 smoke + 60s survival)"
@@ -61,7 +61,7 @@ type = "oneshot_async"
 """
 
 [[files]]
-path = "/usr/lib/init.d/20_greeter.service"
+path = "/etc/init.d/20_greeter.service"
 data = """
 [unit]
 description = "Red Bear greeter service (experimental — Phase 3 user session bring-up)"
@@ -80,7 +80,7 @@ type = "oneshot_async"
 """
 
 [[files]]
-path = "/usr/lib/init.d/30_console.service"
+path = "/etc/init.d/30_console.service"
 data = """
 [unit]
 description = "Console terminals"
@@ -96,7 +96,7 @@ respawn = true
 """
 
 [[files]]
-path = "/usr/lib/init.d/29_activate_console.service"
+path = "/etc/init.d/29_activate_console.service"
 data = """
 [unit]
 description = "Activate fallback console VT"
@@ -111,7 +111,7 @@ type = "oneshot_async"
 """
 
 [[files]]
-path = "/usr/lib/init.d/31_debug_console.service"
+path = "/etc/init.d/31_debug_console.service"
 data = """
 [unit]
 description = "Debug console"