fix(window): compensate Windows text-size scaling in the content-fit resizer

[lshw54]

What

Windows Accessibility "Text size" ≥ 130% clips the app again on 6.0.5 (regression of the problem #257 originally fixed, reported in #339). #337 removed #257's --force-device-scale-factor=1 to fix the oversized-window bug at >100% display scaling and kept --force-text-scale-factor=1 as a text-size guard — but that switch does not exist in Chromium (zero matches in the Chromium source), so it was silently ignored and nothing guarded against text scaling.

Root cause of the clipping: WebView2's rasterization scale is monitor DPI scale × system text scale and is surfaced to the page as devicePixelRatio, while Tauri's LogicalSize multiplies by the window's monitor-DPI scale only. At text size 130%, one CSS px paints 1.3× larger than the logical px fitWindow sized the window in — content overflows the window by exactly that ratio.

Fix

Have both: keep #337's correct display-scaling behaviour AND respect the user's enlarged text (instead of #257's approach of forcing the webview back to 100%, which defeated the accessibility setting).

Derive the text scale at runtime —

textScale = devicePixelRatio / (windowScaleFactor × appliedWebviewZoom)

— and multiply it into every LogicalSize the content-fit resizer emits. The window simply grows to fit the enlarged text. At text size 100% the ratio is 1, so behaviour at every display scaling is byte-identical to #337.

• src/services/windowFit.ts — scale tracking + clamped textScaleFactor() (dependency-free, unit-tested). Clamp to [1, 3]: Windows text size spans 100–225%, so out-of-band values (transient mid-resize readings, persisted Ctrl-zoom-out) fall back to 1.
• src/router/index.ts — track Window.scaleFactor() / onScaleChanged, multiply the factor into fitWindow and resizeWindow, record the zoom fitWindow applies so it can be divided back out of devicePixelRatio.
• src-tauri/src/lib.rs — drop the fictional flag; only set WEBVIEW2_ADDITIONAL_BROWSER_ARGUMENTS when there are real args.
• 10 new vitest specs covering the factor maths (text-only scale, display+text combined, zoom division, clamps, invalid inputs).

Notes for reviewers

• Frontend typecheck / eslint / prettier / vitest (639) and Rust cargo check + clippy all pass.
• A text-scale change re-fits automatically: it changes the rasterization scale → CSS-px viewport shrinks → the existing resize listener fires. No new event wiring needed.
• Like fix(window): correct oversized window at >100% scaling + add Maintenance recovery controls #337, the actual accessibility behaviour needs on-device verification (set Accessibility → Text size to 130–225% and check login + account list) — CI has no scaled desktop.

Closes #339