Implement SessionStore-backed windowed request-list data source

[LocNguyenHuu]

Summary

Follow-up to #28.

Move the main request list from array-backed row projection to a real windowed/paged data source backed by SessionStore.

Why

#28 introduces the row-model seam. This issue completes the next major architecture step: the table should no longer require the full filtered dataset to be materialized as in-memory arrays for large sessions.

This is the core scaling step toward 1M+ rows.

Scope

• Add summary/count/window queries to the production request-list path
• Introduce a window cache for visible and near-visible row ranges
• Back NSTableView from that windowed source instead of full in-memory filtered arrays
• Preserve row identity, selection stability, and native AppKit behavior
• Keep column rendering driven by lightweight row summaries

Must Preserve

• smooth scrolling
• stable selection by UUID
• sort descriptors integration
• custom header columns
• built-in columns from current source
• comments/highlights/pin/save indicators
• inspector opening from selected row

Non-Goals

• full store-backed filtering/sorting logic in this issue
• final lazy detail loading for every action path

Acceptance Criteria

• Table can render from a windowed store-backed source
• Visible row fetches do not require full-array materialization
• Selection remains stable across window changes
• AppKit table interactions still feel native
• Focused tests cover window cache behavior and row identity mapping

Links

• Follows Investigate million-row NSTableView scaling and native table features for the main request list #28
• Depends on Build unified transaction lookup and action routing for live + persisted request-list rows #30
• Blocks store-backed filtering/sorting and lazy detail-loading follow-up work