Add site search (Pagefind)

Client-side index generated after the Hugo build; search box in the
header, results page with a section filter.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YDRjtmAiNpo5mK5N3d7QwZ

Makefile

@@ -1,6 +1,8 @@
 OC ?= ../oc
 # not public/: a running `hugo server` renders there, with its live-reload script
 BUILD ?= build
+# search index generator (https://pagefind.app), fetched by npx on first use
+PAGEFIND ?= npx -y pagefind@1
 # test server: the web share of barbel-lescar, mounted from the file manager (smb://barbel-lescar/web)
 DEPLOY_DIR ?= /run/user/$(shell id -u)/gvfs/smb-share:server=barbel-lescar,share=web/oldcomputers
 DEPLOY_URL ?= https://barbel.synology.me/oldcomputers/
@@ -10,9 +12,10 @@ DEPLOY_URL ?= https://barbel.synology.me/oldcomputers/
 content:       ## regenerate content/ and static/media/ from the extraction repo
 	python3 $(OC)/scripts/05_hugo.py --target $(CURDIR)
 
-build:         ## build the site into $(BUILD)/
+build:         ## build the site and its search index into $(BUILD)/
 	rm -rf $(BUILD)
 	hugo --panicOnWarning --minify -d $(BUILD)
+	$(PAGEFIND) --site $(BUILD)
 
 check: build   ## build, then verify every internal link and image
 	python3 tools/check_links.py $(BUILD)