feat(nostr): ancestor 't' tags on menu listings

When a menu item's NIP-99 kind-30402 listing is published, the
extension now emits one 't' tag per ancestor node name (root-first,
slugified to lowercase ASCII). This lets Nostr clients filter the
global listing stream by category — e.g.
    {"#t": ["hot-beverages"]}
    {"#t": ["coffee-based"]}
without having to know the publisher's pubkey or pull markdown
content. The 'menu' anchor stays first so subscribers can still
get the universal stream. Allergen / ingredient prefixes
(allergen:<x>, ingr:<x>) and dietary tags are unchanged.

nostr_publisher.py:
  - Add _slugify(name) -> str (lowercase, [^a-z0-9]+ -> '-', strip).
  - build_menu_item_event takes ancestor_names: tuple[str, ...] kw
    and emits dedup'd slugs. Stays DB-free; the caller does the
    walk.

views_api.py:
  - _ancestor_names_for_node walks the materialized path of an
    item's node to (root.name, ..., leaf.name).
  - _publish_menu_item passes them to the builder.
  - api_update_menu_node detects a name change and calls
    _republish_subtree_items(node_id), which re-publishes every
    menu_item in the subtree so the new ancestor slug lands on
    each listing. <=50 items per restaurant in practice; eager
    re-publish keeps the relay state consistent without a
    background sync.

nostr_publisher.py

@@ -23,6 +23,7 @@ who don't care about identity separation.
 """
 
 import json
+import re
 import time
 from typing import Optional
 
@@ -33,6 +34,28 @@ from .models import MenuItem, Restaurant
 from .nostr.event import NostrEvent
 
 
+_SLUG_NON_ALNUM = re.compile(r"[^a-z0-9]+")
+
+
+def _slugify(name: str) -> str:
+    """
+    Convert a node name to a lowercase ASCII slug suitable for the
+    Nostr `t` (hashtag) tag. Relays and clients filter on `#t` values
+    by exact match, so 'Hot Beverages' must become 'hot-beverages'
+    for the filter `{"#t": ["hot-beverages"]}` to find it.
+
+    Best-effort:
+      * Lowercase
+      * Replace any run of non-alphanumeric characters with '-'
+      * Strip leading/trailing dashes
+      * Empty / whitespace-only input returns ''
+    """
+    s = (name or "").strip().lower()
+    s = _SLUG_NON_ALNUM.sub("-", s)
+    s = s.strip("-")
+    return s
+
+
 # --------------------------------------------------------------------- #
 # Builders                                                              #
 # --------------------------------------------------------------------- #
@@ -75,7 +98,11 @@ def build_restaurant_metadata_event(restaurant: Restaurant, pubkey: str) -> Nost
 
 
 def build_menu_item_event(
-    item: MenuItem, restaurant: Restaurant, pubkey: str
+    item: MenuItem,
+    restaurant: Restaurant,
+    pubkey: str,
+    *,
+    ancestor_names: tuple[str, ...] = (),
 ) -> NostrEvent:
     """
     Build a NIP-99 classified listing (kind 30402) for a menu item.
@@ -87,13 +114,21 @@ def build_menu_item_event(
       summary   item.description (truncated, optional)
       price     [price, "<amount>", "<currency>"]
       image     each entry in item.images
-      t         "menu", "<category-name>", each dietary tag, each allergen
-                (prefixed `allergen:`), each ingredient (prefixed `ingr:`)
+      t         "menu", each ancestor node name (slugified, root-first),
+                each dietary tag, each allergen (prefixed `allergen:`),
+                each ingredient (prefixed `ingr:`)
       l         "restaurant:<restaurant.id>" (link back to the operator)
       location  restaurant.location (if set)
       g         restaurant.geohash (if set)
       status    "active" | "sold" (NIP-99 standard) — sold-out state
 
+    `ancestor_names` is the chain of node names from the root down to
+    (and including) the item's own node, e.g.
+        ("Drinks", "Hot Beverages", "Coffee-based")
+    Each is slugified to lowercase ASCII so `#t=hot-beverages` filters
+    work cleanly. Caller (views_api._publish_menu_item) walks the
+    materialized path; this builder stays DB-free.
+
     Content is markdown — currently `item.description`; can be expanded
     later to include rich allergen/ingredient blocks.
     """
@@ -109,6 +144,13 @@ def build_menu_item_event(
         tags.append(["summary", item.description[:140]])
     for img in item.images or []:
         tags.append(["image", img])
+    # Ancestor categories — slugified, deduped, root-first.
+    seen_slugs: set[str] = set()
+    for ancestor in ancestor_names:
+        slug = _slugify(ancestor)
+        if slug and slug not in seen_slugs:
+            seen_slugs.add(slug)
+            tags.append(["t", slug])
     for diet in item.dietary or []:
         tags.append(["t", diet])
     for allergen in item.allergens or []: