[P3] Focus Mode / Zoom settings widgets are constructed dynamically in main.gd _ready()

[itsmiso-ai]

Ask: Move the Focus Mode CheckButton and Zoom slider/label from runtime construction in main.gd _ready() into main.tscn (or a settings_panel_builder.gd) so the settings UI is visible in the scene file and restylable without code changes.
Expected files: scripts/main.gd, scenes/main.tscn

Problem: scripts/main.gd _ready() constructs the Focus Mode toggle and Zoom controls at scripts/main.gd:268-296 by calling CheckButton.new(), Label.new(), and HSlider.new(), wiring signal handlers that capture settings/tick_timer via closures, and parenting them to settings_panel.get_node("SettingsMargin/SettingsBox"). Three concerns are mixed: scene composition, persisted-settings round-trip, and tick-timer reconfiguration. Because the widgets are created in code, scenes/main.tscn does not describe them; opening the .tscn cannot reveal what the settings panel looks like, and a refactor of settings_panel.get_node("SettingsMargin/SettingsBox") silently breaks _ready with a null deref. The 2026-07-08 audit (#269 finding 9) flagged this and it has not been addressed.

Evidence:

• scripts/main.gd:268 — comment "Focus Mode and Zoom Controls (Issue Add true focus mode and zoom controls #19)" introduces the runtime construction block
• scripts/main.gd:270 — var focus_mode_btn := CheckButton.new()
• scripts/main.gd:272 — focus_mode_btn.text = "Focus Mode"; focus_mode_btn.toggled.connect(func(val): ... settings['focus_mode'] = val; save_settings(); if tick_timer: tick_timer.wait_time = tick_seconds_for_setting())
• scripts/main.gd:281 — var zoom_label := Label.new()
• scripts/main.gd:285 — var zoom_slider := HSlider.new() wired to Constants.ZOOM_MIN / ZOOM_MAX / ZOOM_STEP with a value_changed handler that mutates settings['zoom_factor'] and rebuilds the zoom label text
• scripts/main.gd:279, 284, 295 — add_child() calls into settings_panel.get_node(...) — path-coupled: changing the scene path silently breaks runtime
• scenes/main.tscn — does not contain the Focus Mode CheckButton, the Zoom label, or the Zoom HSlider; grepping the scene file for "zoom" or "focus" returns nothing
• tests/test_dock_layout.gd — exercises only apply_anchor_layout(); no test exists for the dynamic settings widgets

Acceptance:

• Focus Mode CheckButton, Zoom label, and Zoom HSlider are placed in scenes/main.tscn inside the SettingsBox, each with a unique-name (%FocusModeButton, %ZoomLabel, %ZoomSlider)
• main.gd _ready() references the scene-placed nodes via % unique-name access, retaining the same toggle/value_changed handlers and the same settings persistence semantics
• The runtime construction block is removed from main.gd
• Verify scenes/main.tscn renders the settings panel identically (open the scene in Godot, check Focus Mode + Zoom appear under Settings)