Add Crusader-specific USECODE data and documentation

- Introduced new file `vm_mask_ladder.tsv` containing detailed mappings for Crusader USECODE VM masks and their associated descriptors.
- Added comprehensive documentation in `scummvm-crusader-reference.md` outlining the structure, findings, and implications for reverse-engineering the Crusader engine within ScummVM.
- Created `usecode-roundtrip-ir.md` to document the plan for converting Crusader USECODE bytes into a human-readable format, detailing the container layout, event names, and intrinsic tables.
- Implemented a PowerShell script `temp_usecode_sample.ps1` for extracting and analyzing USECODE data from the Crusader FLX files, providing insights into class and event structures.

.github/agents/ghidra-decomp-mini.agent.md

@@ -3,7 +3,7 @@ description: 'GPT-5 mini agent for low-complexity Crusader decompilation prep, b
 name: 'Ghidra Decomp Mini'
 model: 'GPT-5 mini'
 target: 'vscode'
-user-invocable: true
+user-invocable: false
 ---
 
 # Ghidra Decomp Mini
@@ -38,6 +38,8 @@ Handle small, well-bounded tasks that do not need codex-style execution depth or
 
 If the work is actually mid or high complexity, say so and recommend routing back to the orchestrator or codex lane.
 
+This agent is intended for internal invocation by the user-facing director or its internal orchestrator, not as a normal manual handoff target.
+
 ## Working Rules
 
 - Be conservative and evidence-bound.