Fix: Add locale-independent number parsing for all input methods (#2082)

[ikonnow]

This PR fixes issue #2082 and #2084.

#2082: Locale-independent float parsing

When users enter comma-separated decimal values (e.g., "1,5") in locales where comma is the decimal separator, the application incorrectly parses these values, leading to:

• Negative UI scale values (-1) that crash the application
• Incorrect brush radius values
• General float parsing failures across the UI

Solution

Replace commas with dots before parsing floats in all input methods:

Modified files:

1. base/sources/iron.h - parse_float() function
2. base/sources/iron_ui.c - ui_slider() function (both WITH_EVAL and non-WITH_EVAL paths)
3. base/sources/iron_ui_ext.c - ui_float_input() function
4. base/sources/iron_json.c - JSON parsing (3 locations)
5. base/sources/libs/minic.c - Lexer now recognizes leading-dot float literals (.3, .5f)
6. base/sources/libs/minic_tests.c - Added test13 for leading-dot float literals

#2084: Clamp opacity to [0,1] range

Opacity values could drift outside the valid [0,1] range through the UI and rendering pipeline, causing visual artifacts.

Solution

Clamp opacity after slider input and in uniform reads:

Modified files:

• paint/sources/nodes_brush/brush_output_node.c
• paint/sources/ui/tab_layers.c
• paint/sources/ui/tab_swatches.c
• paint/sources/ui/ui_header.c
• paint/sources/uniforms.c

Testing

• All comma-to-dot and leading-dot float cases verified with standalone test
• Full ArmorPaint Debug x64 build compiles cleanly
• Manual testing confirmed comma-separated values and opacity sliders work correctly

[ikonnow]

Updated the PR description to also include issue #2084 — the branch now contains two related fixes:

1. UI scale accepts negative values causing app to not start - locale issue with comma vs decimal point #2082 — Locale-independent float parsing (comma→dot replacement in iron.h, iron_ui.c, iron_ui_ext.c, iron_json.c, plus minic lexer fix for .3 / .5f literals)
2. Brush opacity can exceed 1.0 causing weird painting behavior #2084 — Clamp brush/layer opacity to [0,1] range

I’ve also reduced the commit history from 7 confusing commits to 2 clear ones to make it easier to review.
I hope this is a bit clearer now so that it can be merged… In my view, these changes make the application usable, at least with my German keyboard. The opacity adjustment can also be found in other tools, such as Krita, etc.

[ikonnow]

Rebased onto latest upstream main — branch is now conflict-free and ready for merge.

• All 11 files clean (no merge artifacts)
• 2 commits: float parsing fix (UI scale accepts negative values causing app to not start - locale issue with comma vs decimal point #2082) + opacity clamping fix (Brush opacity can exceed 1.0 causing weird painting behavior #2084)
• Build-tested and manually verified before each force-push