feat(categories): switch to single-label classification

Each app now gets EXACTLY ONE category - the dominant slug that
best captures its primary identity - instead of up to 3.

Rationale
Multi-label was producing the same app in multiple mobile-shell
swipers (a music+dance+games app would surface in three category
rows), which made the browse surface feel noisy and duplicated.
Single-label gives every app exactly one home, which is what the
mobile category chips and per-category swipers need.

Changes
- MAX_CATEGORIES_PER_APP: 3 -> 1.
- Prompt OUTPUT FORMAT: "Pick EXACTLY ONE slug" instead of "1 to 3".
- STEP 2 of the DECISION ALGORITHM: explicit tie-break guidance
(which slug a user would name FIRST in one word), with concrete
examples (music+dance, storytelling+kids, vision+games).
- Few-shot: Music Quiz example moved from ["music","games","dance"]
to ["music"] to model the tie-break.
- TAXONOMY_VERSION: 2 -> 3 (forces a reclassify on the next boot).

Side effects (positive)
Single-label naturally resolves the two pitfalls that v2 still had:
- `surf-report`: kids hallucination disappears (only voice remains).
- `marionette-js`: dev-tools-combined-with-dance disappears (only
dance remains, since dev-tools is now the SOLE category when used).

Output shape stays `categories: string[]` (always 0 or 1 entry) for
forward compatibility - reverting to multi-label later would be a
prompt change only, no API break.

Co-authored-by: Cursor <cursoragent@cursor.com>

server/categories.js

@@ -33,8 +33,11 @@
  *   - v1: initial 8-slug taxonomy.
  *   - v2: added `games`, tightened `kids` + `dev-tools` descriptions,
  *         switched the prompt to a DECISION ALGORITHM with few-shot.
+ *   - v3: switched from multi-label (up to 3 slugs) to single-label
+ *         (exactly 1 slug). Each app surfaces in exactly one category
+ *         section on the mobile shell - no duplicates across swipers.
  */
-export const TAXONOMY_VERSION = 2;
+export const TAXONOMY_VERSION = 3;
 
 /**
  * Canonical category list. Keep slugs short, kebab-case, and

server/categorize.js

@@ -39,7 +39,13 @@ const DEFAULT_MODEL = 'meta-llama/Llama-3.1-8B-Instruct';
 
 // README budget
 const README_MAX_CHARS = 3000;
-const MAX_CATEGORIES_PER_APP = 3;
+
+// Single-label classification: each app gets EXACTLY ONE slug -
+// the dominant one. The shape stays `string[]` for forward
+// compatibility (if we ever revert to multi-label, no API break),
+// but the array always contains 0 or 1 entry. Mobile chips and
+// "swipers per category" thus surface each app once and only once.
+const MAX_CATEGORIES_PER_APP = 1;
 
 // LLM call budget
 const LLM_TIMEOUT_MS = 30_000;
@@ -175,8 +181,9 @@ const FEW_SHOT_EXAMPLES = [
   [
     'Music Quiz',
     'Play a blind test music game with a dancing Reachy.',
-    ['music', 'games', 'dance'],
-    '(multi-label: three slugs truly co-apply, ordered by relevance)',
+    ['music'],
+    '(single dominant slug - music wins over games/dance because ' +
+      "the app's primary identity is a music blind-test)",
   ],
   [
     'Mime Bot',
@@ -217,9 +224,11 @@ function buildMessages({ name, description, readme }) {
   const system = `You classify a Reachy Mini robot app into a CLOSED list of categories.
 
 OUTPUT FORMAT
-Return ONLY a single JSON object: {"categories": ["slug1", "slug2"]}.
-Pick 1 to ${MAX_CATEGORIES_PER_APP} slugs, ordered from most to least relevant.
-Use the EXACT slug. No prose, no code fences, no commentary outside the JSON.
+Return ONLY a single JSON object: {"categories": ["slug"]}.
+Pick EXACTLY ONE slug - the single dominant category that best
+captures the app's primary identity. Use the EXACT slug. The list
+always contains 0 or 1 entry.
+No prose, no code fences, no commentary outside the JSON.
 
 DECISION ALGORITHM (apply in order)
 
@@ -231,13 +240,20 @@ raw remote-control interface, dev-only test space.
 Examples that DO NOT pass the veto (they are user-facing apps):
 TTS players, voice chat, music apps, storytelling, companions -
 even when the README is dev-heavy.
-  - YES -> return {"categories": ["dev-tools"]} and STOP. Never combine.
+  - YES -> return {"categories": ["dev-tools"]} and STOP.
   - NO  -> continue to STEP 2.
 
-STEP 2 - Pick 1 to ${MAX_CATEGORIES_PER_APP} user-facing slugs from the
-list below. Choose the MOST SPECIFIC categories. Order from most to
-least relevant. Multi-label is encouraged when two categories truly
-co-apply (e.g. music-and-dance, kids storytelling, vision game).
+STEP 2 - Pick the SINGLE most dominant user-facing slug from the list
+below. Choose the slug that captures the app's primary identity, not
+every aspect it touches. When two slugs feel equally fitting, pick the
+one that a user would name FIRST when describing the app in one word.
+Examples of tie-breaks:
+  - music + dance app -> prefer \`music\` if the user picks the song,
+    \`dance\` if the choreography is the point.
+  - storytelling + kids app -> prefer \`kids\` if it explicitly targets
+    children, \`storytelling\` otherwise.
+  - vision + games app -> prefer \`games\` if there is a play loop,
+    \`vision\` if it is mostly a perception demo.
 If the README is empty or very sparse, USE THE NAME AND DESCRIPTION
 as the primary signal - do not bail to an empty list just because the
 README is thin.