macOS: Dictation (voice input) silently drops text — selectedRange returns NSNotFound

Description

Summary
On macOS, dictated text never reaches the focused winit window. The system dictation UI (mic icon / flyout) activates and shows recognized words, but nothing is inserted into the app.

Root cause
macOS dictation delivers transcribed text through the same NSTextInputClient path used for IME composition — via insertText:replacementRange: — but only after confirming a valid insertion point by querying selectedRange. Winit's macOS NSView implementation (src/platform_impl/macos/view.rs) returns NSNotFound from selectedRange rather than a real range. macOS interprets NSNotFound as "no valid cursor position" and discards the dictated text before ever calling insertText:replacementRange:.

This appears to be the same underlying gap tracked in #3617 ("selected_range and replacement_range parameters are ignored"), surfacing here specifically as a dictation regression rather than an IME composition bug.

Expected fix
Have selectedRange in winit's NSTextInputClient impl return a valid NSRange (e.g. NSRange::new(0, 0) when there's no real selection tracking) instead of NSNotFound. Ideally firstRectForCharacterRange: should also return a real rect so the dictation indicator positions correctly near the cursor, but the selectedRange fix alone is what unblocks text delivery.

Impact
Affects every winit-based macOS app that hasn't separately worked around this (Neovide, Alacritty-style terminals, etc.) — accessibility-relevant, since dictation is a primary input method for some users.

macOS version

mac os
26.6.1

Winit version

0.30.13

Start in src/platform_impl/macos/view.rs and inspect the NSTextInputClient implementation, especially selectedRange. Confirm how the current NSNotFound result affects macOS dictation, then make selectedRange return a valid range as described in the issue. Verify that dictated text reaches the focused winit window; firstRectForCharacterRange: is an optional follow-up for indicator positioning.