Add pluggable storage, node tags, and HTML export

[antra-tess]

Summary

• Pluggable storage abstraction with LoomStorage interface — LegacyStorage (existing monolithic data.json) and DocumentStorage (per-document .loom.json files alongside markdown). Includes migration tool with confirmation modal.
• Node tag system replacing the bookmarked boolean with a flexible tags: string[] array. Ships with quick tags (fav, to_continue, private) with emoji indicators, tag-based filtering (+include -exclude syntax), and a favorites sidebar section. Legacy bookmarked nodes are auto-migrated to the fav tag.
• HTML export producing self-contained interactive HTML files with two-panel layout, collapsible tree, node type indicators, tag color coding, and embedded metadata.
• AWS Bedrock provider support.
• Extended node metadata: nodeType, createdTimestamp, generationModel, generationParameters for tracking node provenance.
• Developer mode setting for debug logging.

Test plan

• Fresh install: verify plugin loads with default (legacy) storage
• Create nodes, verify tags: [] instead of bookmarked: false
• Toggle tags via right-click menu and hover buttons
• Tag filtering: type +fav -private in filter bar
• Enable document storage in settings, run migration, verify .loom.json files appear
• Switch back to legacy storage and verify data preserved
• Export HTML via command palette, verify interactive file opens in browser
• Rename a markdown file with document storage enabled, verify .loom.json follows

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