Make TagSelector tooltip mode-aware for comma-separated tags

[Copilot]

The tooltip was updated to only mention 'everything' tag but removed the comma-separated tags functionality hint. Users in create mode can still add multiple tags at once using commas but had no UI indication of this.

Changes

• Added tooltipText computed property that generates contextual help based on mode and allowEverything props
• Tooltip now shows comma-separated help in create mode, 'everything' tag info when allowed, or both
• Icon hidden when no relevant tooltip text applies

Tooltip Text by Context

Mode	allowEverything	Tooltip
create	true	"Add multiple tags using commas. 'everything' tag covers all possible tags"
create	false	"Add multiple tags using commas"
search	true	"'everything' tag covers all possible tags"
search	false	(hidden)

const tooltipText = computed(() => {
    const parts = [];
    if (props.mode === 'create') {
        parts.push("Add multiple tags using commas");
    }
    if (props.allowEverything) {
        parts.push("'everything' tag covers all possible tags");
    }
    return parts.join('. ');
});

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