feat: cell-detail right-hand drawer horizontal resize (#101)

[BorisTyshkevich]

What & why

Closes #101. Adds a drag handle to the right-hand cell-detail / rows-viewer drawer's left edge (.cd-panel, src/ui/results.js), shared by openCellDetail and openRowsViewer, so users can widen it to comfortably read long values/rows. Reuses splitters.js's drag controller (a new 'drawer' axis alongside col/sideRow/row) rather than a third bespoke resize implementation, per the issue's guidance. Width is clamped to 320px..92vw and persisted as cellDrawerPx — one shared value for both drawers.

Fixes the issue's flagged correctness catch: finishing a resize drag with the mouse released over .cd-backdrop (not .cd-panel) previously closed the drawer, since the browser's post-mouseup click targets the nearest common ancestor of the mousedown/mouseup targets, bypassing the panel's own stopPropagation. A one-shot capturing click listener installed at drag-start swallows exactly that click.

Code review (8-angle parallel pass) surfaced one additional, real gap beyond the issue's own scope: closing the drawer mid-drag (e.g. pressing Escape while the mouse button is still down, before the drag's own mouseup/click ever fires) left the drag's mousemove/mouseup/click-swallow listeners attached after the panel was removed — a later, completely unrelated mouseup would still persist a stale cellDrawerPx, and a later unrelated click would be silently swallowed. Fixed: startDrag now returns a cancel(), wired into both drawers' close(), which also reverts the width to its pre-drag value.

A broader, pre-existing pattern was found and filed separately rather than fixed here (out of scope for a resize-handle issue): .cd-backdrop's onclick:close doesn't check where the corresponding mousedown originated, so e.g. dragging a text selection past the panel edge has the same close-on-drag-release bug — see #110, deferred to the planned shared Drawer primitive (#60).

Verified live against a real ClickHouse cluster (npm run local + Playwright): drag-resize, clamp bounds, persistence across reload, no-close-after-drag, and the Escape-mid-drag cancel path all confirmed working, including the zoom-scale compensation math (this app's html{zoom} factor was non-1 in the test viewport, and the handle tracked the cursor 1:1 regardless).

Checklist

• npm test passes (the per-file coverage gate is non-negotiable)
• Tests added/updated in the same change as the code
• npm run build succeeds (single-file dist/sql.html)
• Layers kept honest: pure logic in src/core/, network in src/net/ (injected fetch), DOM in src/ui/
• No new runtime dependency
• README / CHANGELOG.md ([Unreleased]) updated
• Reconciled affected tracked work (roadmap Roadmap to 1.0.0 #68, issue Cell-detail right-hand drawer: add horizontal resize #101 body — both updated; filed Backdrop-closes-on-any-click doesn't check gesture origin (drag/selection past the panel edge closes it) #110 for the broader backdrop-close pattern found along the way)

Test plan

• npm test — 1272 tests, 100% coverage gate green
• npm run build — dist/sql.html builds
• npm run test:e2e — 39 Playwright tests (chromium/firefox/webkit) green
• Manual verification against a live ClickHouse cluster via npm run local + Playwright (see PR description)

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