feat: implement smart notebook & tag apply, undo, and empty notebook cleanup

[Harsh16gupta]

Overview

This PR implements the note categorization application layer, allowing users to apply folder organizations and smart semantic tags to notes in one click, revert changes (Undo), and clean up empty original notebook folders.

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Key Features

1. Unified Apply Action: Moves notes to cluster folders and applies tags in a single unified action.
2. Smart Tag Matching: Automatically matches cluster keywords against each note's title/body and tags the note only if the keyword actually appears inside it.
3. Empty Folder Clean Up: Deletes original notebook folders if they became empty of notes and subfolders after categorization.
4. Revert (Undo): Restores notes to their original notebooks and deletes applied tags cleanly.
5. Lock Guard: Prevents concurrent apply, undo, or cleanup operations to avoid conflicts.

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Performance & Safety Optimizations

• Unified Note Queries (2x Speedup): Fetches parent IDs, titles, and bodies in a single database call per note.
• In-Memory Caches (10x-100x Speedup): Maps existing tags and folders at startup to replace nested database query loops with $O(1)$ Map lookups.
• Safer Undos: Folder restoration skips deleting folders if they contain any notes or subfolders, and handles deleted parent folders gracefully.

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Screen Recording:

Screencast.From.2026-07-07.17-53-33.mp4

[Copilot]

Pull request overview

This PR adds an “application layer” to the plugin so users can apply categorization results (move notes + apply semantic tags), undo the last apply via a persisted change log, and optionally clean up original notebooks that became empty. It also adds corresponding UI controls and plugin-side settings to support these operations.

Changes:

• Adds apply/undo/cleanup commands and a persisted categorization.changeLog state to support revert and cleanup workflows.
• Extends the webview state machine and UI (Dashboard + History) to trigger and monitor apply/undo/cleanup progress and results.
• Introduces new message types (apply, undo, cleanUpEmptyNotebooks, settings get/update) to coordinate between webview and plugin.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/webview/panel.css	Adds styling for Apply/Undo/Cleanup UI controls and status banners.
src/webview/pages/HistoryPage.tsx	Implements a History view that surfaces undo/cleanup actions and status based on stored change log.
src/webview/pages/DashboardPage.tsx	Adds “Apply categorization” UI + wires up apply state/progress/error handling.
src/webview/context/AppStateContext.tsx	Adds settings fetch/update and apply/undo/cleanup state + polling handling in the app state context.
src/types/panel.ts	Adds ApplyOptions, ApplyMessage, and new panel message types for apply/undo/cleanup + settings.
src/index.ts	Registers plugin settings and routes new webview messages to apply/undo/cleanup background operations with a lock guard.
src/commands/applyChanges.ts	New core implementation for apply, undo, and cleanup (tag matching, moving notes, change log persistence).

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[Harsh16gupta]

All the review comments have been addressed except the one about the parent notebook (#26 (comment)).

[HahaBill]

lgtm