refactor: remove QMD semantic indexing — keep keyword search only

Remove the entire QMD search engine (semantic indexing, hybrid search,
vector embeddings) and replace with a simple walkdir-based keyword
search. QMD never worked reliably in production, added bundle bloat,
and showed "Index failed" in the status bar.

What changed:
- Rust: deleted indexing.rs, rewrote search.rs as pure keyword search
- Frontend: removed useIndexing hook, IndexingBadge, hybrid search
- Menu: removed "Reindex Vault" command from palette and menu bar
- Config: removed qmd from bundle resources and build script
- Deleted tools/qmd/ (QMD CLI tool, MCP server, tests)
- Updated docs (ARCHITECTURE, ABSTRACTIONS, GETTING-STARTED)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/hooks/useAppCommands.ts

@@ -64,7 +64,6 @@ interface AppCommandsConfig {
   onEmptyTrash?: () => void
   trashedCount?: number
   onReopenClosedTab?: () => void
-  onReindexVault?: () => void
   onReloadVault?: () => void
   onRepairVault?: () => void
   onSetNoteIcon?: () => void
@@ -156,7 +155,6 @@ export function useAppCommands(config: AppCommandsConfig): CommandAction[] {
     onResolveConflicts: config.onResolveConflicts,
     onViewChanges: viewChanges,
     onInstallMcp: config.onInstallMcp,
-    onReindexVault: config.onReindexVault,
     onReloadVault: config.onReloadVault,
     onRepairVault: config.onRepairVault,
     onEmptyTrash: config.onEmptyTrash,
@@ -212,7 +210,6 @@ export function useAppCommands(config: AppCommandsConfig): CommandAction[] {
     onInstallMcp: config.onInstallMcp,
     onEmptyTrash: config.onEmptyTrash,
     trashedCount: config.trashedCount,
-    onReindexVault: config.onReindexVault,
     onReloadVault: config.onReloadVault,
     onRepairVault: config.onRepairVault,
     onSetNoteIcon: config.onSetNoteIcon,