M2: Payload presets and bounded bulk execution

[NickCrew]

Description

Add payload-set management and bulk execution engine so operators can run batches with configurable concurrency and delay while preserving platform safety.

Acceptance Criteria

• Close P0/P1 cluster test gaps from test-review audit #1 Payload presets are available by category and can be selected/deselected for a run.
• Add automated tests for HUD overlay stats, persistence, and keyboard drag behavior #2 Bulk execution endpoint supports bounded concurrency, per-request pacing, and hard limits to prevent uncontrolled traffic.
• Refactor HUD overlay into smaller hooks/components and reduce hardcoded geometry #3 Execution results include per-payload outcome records with status, timing, and error details where applicable.
• Live Payload Fuzzer initiative (Fuzzing Lab) #4 Dashboard supports initiating batch runs and viewing rolling result updates.
• M2: Payload presets and bounded bulk execution #5 Automated tests verify batching behavior, concurrency bounds, and error handling semantics.

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Migrated from backlog TASK-13.2 (Apparatus).