Split launcher, hotkey and windows-layout into parse/plan/exec and platform modules

[multiplex55]

Motivation

• Reduce surface area of code that performs OS side effects by isolating pure parsing and planning logic into testable modules.
• Make hotkey parsing and normalization unit-testable separately from the runtime listener.
• Centralize Windows-specific adapters (mouse position, mocks) to a platform area so platform calls are isolated and easier to mock.

Description

• Split src/launcher.rs into three pieces: src/launcher/parse.rs (action classification and parse_action_kind), src/launcher/plan.rs (pure plan_action/LaunchPlan), and src/launcher/exec.rs (side-effectful execution, launch_action delegates to execute_plan); updated src/launcher.rs to re-export the new surface.
• Split src/hotkey.rs into src/hotkey/parse.rs (pure parse_hotkey, parse_key, parser tests) and src/hotkey/runtime.rs (listener, HotkeyTrigger/HotkeyListener and runtime helpers), keeping src/hotkey.rs as a thin façade exporting the parse/runtime API.
• Extract Windows mouse-position/mocks into a new src/platform/windows_api.rs and added pub mod platform; in src/lib.rs, then re-exported platform helpers from src/window_manager.rs so existing callers continue to work.
• Split src/windows_layout.rs into a small façade plus src/windows_layout/plan.rs with pure matching/score/selection logic (is_rule_match, match_score, restore_plan_select_best and unit tests) and src/windows_layout/apply.rs for applying plans (keeps runtime side effects).
• Added targeted unit tests: hotkey parser tests in hotkey/parse.rs, launcher planning tests in launcher/plan.rs, and layout rule scoring / best-candidate selection tests in windows_layout/plan.rs.

Testing

• Ran cargo fmt as part of the work (code formatting/fixups applied).
• Started cargo check --lib / dependency build to validate the changes, but the full compile was not allowed to complete before handoff so a full build verification is not claimed.
• Added and exercised unit tests for the pure logic (hotkey parser, launcher planning, layout match scoring) in their respective modules; these tests were written and committed but a complete cargo test run was interrupted during the session.

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Codex Task