Add 'Select card to update' action for targeted Anki card updates

[thntx]

Closes #776

Summary

• Adds a new "Select card to update" post-mine action that opens a search dialog when mining, letting the user pick which existing Anki note to update with audio/screenshot instead of always targeting the most recently added card.
• Adds a new update-selected-card keyboard shortcut (Chrome extension command) that triggers this action directly.
• The dialog shows the last 50 notes added in the past 30 days, displays the note's key field (field with order === 0) as the primary label and the configured sentence field as secondary, and supports live search filtering across both.
• A multi-select checkbox (off by default, persisted via localStorage) lets the user select multiple cards and apply the update to all of them at once via an "Apply (N)" button.
• Fullscreen is gracefully handled: the dialog exits fullscreen, shows, then re-enters fullscreen on close.
• Locale fix: bundled strings are now deep-merged as the base with cached remote translations on top, so new locale keys are never missing even when an older cached version is present.

Test plan

• Set "Post-mine action" to "Select card to update" in extension settings
• Mine a subtitle line — dialog should appear listing recent Anki notes
• Search filters correctly by key field and sentence field
• Single-click on a note updates it with audio/screenshot and closes dialog
• Enable multi-select checkbox → select multiple notes → "Apply (N)" updates all of them
• Multi-select preference persists across dialog opens
• Dialog appears and closes correctly when video is in fullscreen
• New keyboard shortcut appears after "Update last card" in chrome://extensions/shortcuts
• All UI strings display correctly (no raw i18n keys)

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