fix: keyboard feedback #1644 (#1697)

Addresses reviewer feedback from #1644:
- **Localize keyboard hint strings** — 13 hardcoded English strings
replaced with \`tr()\` macro (\`STR_KB_HINT_*\`), making them
translatable across all 22 languages (fallback to English when not yet
translated)
- **Deduplicate \`Lyra3CoversMetrics\`** — now derives from
\`LyraMetrics\` via lambda copy, overriding only \`homeCoverTileHeight\`
and \`homeRecentBooksCount\` (eliminates ~30 duplicated metric fields)
- **Unify keyboard drawing in \`BaseTheme\`** — \`drawTextField\` and
\`drawKeyboardKey\` overrides removed from \`LyraTheme\`; variability
controlled via \`keyboardKeyCornerRadius\` metric (0=Base, 6=Lyra).
Unified text field padding to 6, adopted Lyra's secondary label draw
order (main first, then secondary)
- **Add URL-optimized keyboard layout** — \`urlLayout\` with \`:\` and
\`/\` replacing \`=\` and \`,\` for easier URL input without switching
to SYM mode
---

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lib/I18n/translations/english.yaml

@@ -583,3 +583,18 @@ STR_BTN_ACT_PREV_SECTION: "Previous Section / Chapter"
 STR_BTN_ACT_EXIT_READER: "Exit Reader"
 STR_BTN_ACT_READER_MENU: "Reader Menu"
 STR_BTN_ACT_KOREADER_SYNC: "KOReader Sync"
+STR_KB_HINT_MOVE_CURSOR: "Press LEFT or RIGHT to move cursor"
+STR_KB_HINT_RETURN_CURSOR: "Press LEFT to return to cursor position"
+STR_KB_HINT_HIDE_PASSWORD: "Hold RIGHT then press [***] to hide password"
+STR_KB_HINT_SHOW_PASSWORD: "Hold RIGHT then press [abc] to show password"
+STR_KB_HINT_TOGGLE_HIDE_PASSWORD: "Press [***] to hide password"
+STR_KB_HINT_TOGGLE_SHOW_PASSWORD: "Press [abc] to show password"
+STR_KB_HINT_EDIT_ENTRY: "Hold UP to edit entry"
+STR_KB_TIPS: "Tips:"
+STR_KB_HINT_RETURN_KEYBOARD: "Press DOWN to return to keyboard"
+STR_KB_HINT_EXIT_URL_MODE: "Press ABC to exit URL mode"
+STR_KB_HINT_CLEAR_TEXT: "Hold DEL to clear all text"
+STR_KB_HINT_SECONDARY_CHAR: "Hold SELECT for secondary char"
+STR_KB_HINT_UPPER_SECONDARY: "Hold SELECT for UPPERCASE or secondary char"
+STR_KB_HINT_LOWER_SECONDARY: "Hold SELECT for lowercase or secondary char"
+STR_KB_HINT_URL_SNIPPETS: "Press URL for snippets"