refactor: grid internals and controllers

[rkaraivanov]

Reduce duplication and indirection across /src with no behavior or public API changes:

• Factor the shared emit -> commit -> emit flow in FilterController into a single helper.
• Collapse the six navigation handlers into two clamped movement primitives.
• Extract the slotted-column scan in the grid, shared by slot change and column detection.
• Add resolveCondition() to replace the repeated operand lookup casts in grid, filter controller and filter row.
• Unify the active/inactive chip rendering in the filter row.
• Drop needless indirection: pipeline getters, tree iterator generator, sort direction Map, first-render branch in partMap.
• Flatten nested ternaries in header sort rendering and the filter row state preview; extract a shared adopt-styles predicate.