feat(api): unified FTS search

Single GET /api/search?q=&space_id=&kinds=&limit=&offset= unions FTS
hits across pages / refs / source_docs / messages with a `kind`
discriminator and ts_rank ordering. Each branch's to_tsvector matches
the GIN index expression on its source table so indexes are used.
Messages have no space_id and are excluded when a space filter is set.
Hybrid vector / RRF lands in Plan 3.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

lib/api/routes/search.js

@@ -0,0 +1,37 @@
+import { Router } from 'express';
+import { z } from 'zod';
+import * as repo from '../../db/repos/search.js';
+import { parsePagination } from '../pagination.js';
+import { validate } from '../validate.js';
+import { asyncWrap } from '../errors.js';
+
+const KINDS = ['page','ref','source_doc','message'];
+
+const querySchema = z.object({
+  q: z.string().min(1),
+  space_id: z.string().uuid().optional(),
+  kinds: z.string().optional(),
+  limit: z.string().optional(),
+  offset: z.string().optional()
+});
+
+export const router = Router();
+
+// Hybrid vector + reciprocal-rank-fusion search lands in Plan 3 (see
+// docs/superpowers/specs/2026-05-31-void-v2-design.md §search).
+router.get('/',
+  validate({ query: querySchema }),
+  asyncWrap(async (req, res) => {
+    const { limit, offset } = parsePagination(req);
+    const rawKinds = req.validatedQuery.kinds;
+    const kinds = rawKinds
+      ? rawKinds.split(',').map(s => s.trim()).filter(k => KINDS.includes(k))
+      : null;
+    res.json(await repo.fts({
+      q: req.validatedQuery.q,
+      space_id: req.validatedQuery.space_id ?? null,
+      kinds,
+      limit, offset
+    }));
+  })
+);