[UX] Focus indicators — double border + dimmed inactive panes

[fissible]

Summary

It is currently unclear what is focused, what keys apply, and how to move focus to another area. This affects every screen in the app.

Problems

• Focused and unfocused panes look nearly identical
• No visual affordance tells the user which pane owns keyboard input
• Single border is used for all panes regardless of focus state
• Default terminal white is used for focus highlight

Proposed rules (global)

Focused element (or nearest container)

• Double-line border
• Active theme color (bold or accent)

Everything else

• Single border
• Dimmed (\033[2m) or muted theme color
• Never pure white as a default focus indicator

No-theme fallback: active = white/bold, inactive = dim/default

Scope

All focusable panes: Schema browser (Tables, DDL), Table view (Structure, Data, Query), Welcome screen list.

Implementation notes

• SHELLFRAME_PANEL_FOCUSED is already passed to shellframe_panel_render — border style should change based on this flag ("double" focused, "single" unfocused)
• Theme variables: add SHQL_THEME_PANEL_STYLE_FOCUSED (default "double") alongside existing SHQL_THEME_PANEL_STYLE
• Dimming inactive content: render functions apply $SHELLFRAME_DIM / $SHELLFRAME_RESET around unfocused region content

Files

• src/theme.sh — new focused/unfocused theme variables
• src/screens/schema.sh, table.sh, query.sh, welcome.sh — use focused style in render

Effort

S (1–2h)

[fissible]

Implemented in caafd55:

• Schema sidebar/detail panels switch single↔double border based on focus state
• DDL text dims when schema detail pane is not focused
• Table structure tab text dims when body region is not focused
• SHQL_THEME_PANEL_STYLE_FOCUSED added to both themes (basic: double, uranium: double)