Fix search performance regression and TUI race condition (#262)

Tested and ran into a bunch of performance & context issues that
surfaced in the TUI. Original approach using ILIKE is better it seems
like for large archives. (Note this is a resubmission of #256)

Changes

- Reverts DuckDB text search from regexp_matches to ILIKE — regexp
caused significant performance regression on Parquet scans. ILIKE is
natively optimized by DuckDB for columnar data. FTS5 deep search path is
unchanged.
- Fixes a TUI race condition where pressing a (all messages) then
quickly searching could cause the stale loadMessages response to
overwrite search results. Search now invalidates pending loads via
loadRequestID.
- Fixes a placeholder/arg count drift in buildStatsSearchConditions —
text terms emit 4 args each (subject + snippet + 2 sender) but the
arg-slicing helper assumed 3. Extracted buildNonTextSearchConditions to
eliminate the brittle offset math entirely. Regression tests lock the
placeholder invariant across both search builders.

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Co-authored-by: Wes McKinney <wesmckinn+git@gmail.com>

Author: 3 people

Makefile

@@ -12,7 +12,7 @@ LDFLAGS := -X github.com/wesm/msgvault/cmd/msgvault/cmd.Version=$(VERSION) \
 
 LDFLAGS_RELEASE := $(LDFLAGS) -s -w
 
-.PHONY: build build-release install clean test test-v fmt lint lint-ci tidy shootout run-shootout install-hooks help
+.PHONY: build build-release install clean test test-v fmt lint lint-ci tidy shootout run-shootout install-hooks bench help
 
 # Build the binary (debug)
 build:
@@ -92,6 +92,10 @@ install-hooks:
 tidy:
 	go mod tidy
 
+# Run benchmarks (query engine smoke test)
+bench:
+	go test -tags fts5 -run=^$$ -bench=. -benchtime=1s -count=1 ./internal/query/
+
 # Build the MIME shootout tool
 shootout:
 	CGO_ENABLED=1 go build -o mimeshootout ./scripts/mimeshootout
@@ -117,5 +121,6 @@ help:
 	@echo "  install-hooks  - Install pre-commit hook via prek"
 	@echo "  clean          - Remove build artifacts"
 	@echo ""
+	@echo "  bench          - Run query engine benchmarks"
 	@echo "  shootout       - Build MIME shootout tool"
 	@echo "  run-shootout   - Run MIME shootout"