fix(linux): seek paging, lazy tab restore, grid speed, narrow bottom bar

[datlechin]

• Paging: new core read_page pages past the edge row's key (AfterKey/BeforeKey) and reads Last backward from the end. A PostgreSQL table with no key walks heap block windows that double when short, so no read sorts the whole table. OFFSET stays under a user sort, a restored deep offset and a partitioned keyless table.
• An unsorted export of a keyless table drops ORDER BY ctid.
• Docker tests page a 60k-row keyless table (with deleted rows) and a 25.5k-row keyed table both ways, check every row once in order, and assert a Tid Range Scan or Index Scan Backward plan with no Seq Scan or Sort.
• Session restore: saved tabs open unselected and read their table the first time they are shown, instead of all at once on the 4-connection pool.
• Grid: Select All plus refresh restores the selection in one pass; column widths measure only added rows and cache the digit width; cell text capped at 1,000 characters; cell tint stops scanning edits and copying the pending value; text sort keys use the first 4,096 characters.
• Discard asks first on the browse and structure tabs, like F5.
• The Rows dropdown lists a page size set in Preferences.
• The browse tab is an AdwBreakpointBin: below 680sp, Export, Filter, Count Rows and Rows per Page move into a More menu, and the bar fits the 360 px floor.
• A filter error stays on the stale banner or error page instead of a toast; Count Rows shows it on Try Again.
• Pager says "No rows" or "No rows match the filter"; the structure tab says "unsaved change" like the browse tab.
• Tests changed on purpose: last_page_waits_for_an_exact_total, discard_restores_without_phantom_ops, and two that asserted filter-error toasts.