Add Puzzle #6: Perbug Sequence Forge (node-seeded, modular sequence puzzle)

[ercmine]

Motivation

• Introduce a sixth, modular puzzle type (Perbug Sequence Forge) that plugs into the existing node/puzzle lifecycle and is deterministically seeded from node latitude/longitude.
• Provide a sequence-focused puzzle family supporting numeric and symbolic rules, transformation layers, concealed steps, and plausibly misleading decoys to enable varied difficulty tuning.
• Reuse and extend the shared puzzle framework so future sequence/math/logic variants can plug into the same generator/session/result model without duplicating abstractions.

Description

• Add a lightweight shared puzzle framework with stable seed derivation from node id + lat/lng, puzzle instance/session/result models, difficulty model, and a generator interface (app/lib/features/home/puzzles/puzzle_framework.dart).
• Implement the Sequence Forge generator module with deterministic family selection, multi-layered rule generators (arithmetic, multiplicative, alternating, symbolic cycle), hidden-step placement, deterministic answer choice / decoy generation (with optional misleading symmetry), difficulty knob weighting, debug metadata and submission validator (app/lib/features/home/puzzles/sequence_forge_puzzle.dart).
• Wire Sequence Forge into the Perbug flow by extending PerbugGameState to hold puzzle session state and events, adding lifecycle actions (generate, start, select answer, submit, reset, abandon), telemetry & simple reward hook in PerbugGameController, and a polished in-page UI section to generate/show difficulty and solve the puzzle (app/lib/features/home/perbug_game_models.dart, app/lib/features/home/perbug_game_controller.dart, app/lib/features/home/perbug_game_page.dart).
• Register the new puzzle type in a registry and add focused unit tests that assert determinism, difficulty scaling, hidden-index validity, decoy quality, and validator correctness (app/lib/features/home/puzzles/puzzle_registry.dart, app/test/sequence_forge_puzzle_test.dart).

Testing

• New automated tests were added covering deterministic generation, node variance, difficulty score response to knobs, hidden-index validity and decoy uniqueness, and submission validation (app/test/sequence_forge_puzzle_test.dart and updated app/test/perbug_game_models_test.dart).
• Tests were not executed in this environment because Flutter tooling is not available here (flutter: command not found), so no test run succeeded or failed in this rollout.
• To run the added tests locally or in CI, run: cd app && flutter test test/sequence_forge_puzzle_test.dart test/perbug_game_models_test.dart.

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