Add a search box module and a search page

Readers had no way to find a post. The new "search" module goes in the
header (a bar under the nav) or a side column (a box with a heading) and
is a plain GET form to /search, so it works without JavaScript. The
results page lists the published posts of every page whose title or
Markdown body matches the query — case-insensitive, each word literal,
spaces meaning "anything in between", in order — as title, date and a
short snippet with the match marked, 20 per page.

modules.kind is a CHECK constraint, so a migration widens it; "search"
becomes a reserved page slug so the literal route keeps winning over
/{page}. moduleHasSettings now takes the module: a header search box
has no heading, hence nothing to edit.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Sd8UPWrvyYCLj97JexNw3A

1 files changed, 10 insertions, 6 deletions

diff --git a/internal/web/layout.go b/internal/web/layout.go
index b8069a0..0d51068 100644
--- a/internal/web/layout.go
+++ b/internal/web/layout.go
@@ -12,9 +12,9 @@ import (
 // Modules a blogger can put in each area. Header modules are the big
 // blocks; the side columns take the small boxes; the footer its own set.
 var moduleKinds = map[string][]string{
-	"header": {"title", "logo", "menu"},
-	"left":   {"menu", "recent", "archive", "tags", "tagcloud", "logo", "html"},
-	"right":  {"menu", "recent", "archive", "tags", "tagcloud", "logo", "html"},
+	"header": {"title", "logo", "menu", "search"},
+	"left":   {"menu", "search", "recent", "archive", "tags", "tagcloud", "logo", "html"},
+	"right":  {"menu", "search", "recent", "archive", "tags", "tagcloud", "logo", "html"},
 	"above":  {"html"},
 	"below":  {"html"},
 	"footer": {"text", "rss", "sitemap", "html"},
@@ -29,6 +29,7 @@ var moduleNames = map[string]string{
 	"recent":   "Recent posts",
 	"tags":     "Tags",
 	"tagcloud": "Tag cloud",
+	"search":   "Search box",
 	"html":     "Custom HTML",
 	"rss":      "RSS link",
 	"text":     "Footer text",
@@ -52,11 +53,14 @@ func allowedKind(area, kind string) bool {
 	return false
 }
 
-// moduleHasSettings says whether the module has an edit page.
-func moduleHasSettings(kind string) bool {
-	switch kind {
+// moduleHasSettings says whether the module has an edit page. Header modules
+// show no heading, so a search box there has nothing to edit.
+func moduleHasSettings(m store.Module) bool {
+	switch m.Kind {
 	case "html", "text", "recent", "archive", "sitemap", "tags", "tagcloud":
 		return true
+	case "search":
+		return m.Area != "header"
 	}
 	return false
 }