docs: Obsidian-style vault under docs/

Add a navigable Obsidian vault as the project's first-class
technical documentation. Notes cross-reference with [[wikilinks]];
docs/index.md is the Map of Content.

New notes:
  index.md             MOC, entry point
  architecture.md      what the extension owns vs what lives outside
  data-model.md        entity-by-entity schema reference
  menu-tree.md         the arbitrary-depth tree concept
  order-flow.md        state machine + invoice listener + print
  nostr-layer.md       kinds 0/30402/5/1059, signing, t-tags
  api-reference.md     endpoint catalog by audience
  cms.md               Vue 3 + Quasar 2 UMD conventions, q-tree
  webapp-integration.md  multi-restaurant cart pattern + atomicity
  glossary.md          domain terms

Existing notes (kept as-is):
  adr-0001-menu-tree.md  the storage choice rationale
  design-conversation.md trimmed transcript

README.md adds a Documentation section pointing at docs/index.md
with the headline note list. Each note links to ~3-5 others; the
vault forms a connected graph.

A project-level memory rule (saved outside the repo) commits us to
keeping these docs in sync as the code evolves: any commit that
materially changes schema, API, order flow, Nostr surface, CMS
conventions, or webapp integration must update the relevant note(s)
in the same commit.

docs/glossary.md

@@ -0,0 +1,80 @@
+# Glossary
+
+Domain terms used throughout the docs. Linked from many notes.
+
+**Aggregator** — a webapp / client that pulls menus from multiple
+restaurants and presents them as a single experience (festival, food
+court, collective space). Aggregators live outside this extension.
+
+**Ancestor chain** — the ordered list of node names from the root of
+the [[menu-tree]] down to (and including) a given node. Slugified
+versions of these names ride along on every Nostr menu listing as
+`t` tags so [[nostr-layer|clients can filter]] without parsing
+markdown.
+
+**Cascade detach** — the default behavior when deleting a
+[[menu-tree|menu node]] that has items: the items are
+**detached** (their `node_id` is set to NULL) rather than
+hard-deleted. They survive as orphans for the operator to re-home
+through the [[cms]]. Hard delete is opt-in.
+
+**CMS** — the operator console. Server-rendered Jinja templates +
+inline Vue 3 / Quasar 2 UMD. See [[cms]].
+
+**Customer pubkey** — the Nostr pubkey of an ordering customer.
+Optional metadata on `orders.customer_pubkey`. Used for sending
+status updates back via [[nostr-layer|NIP-17 DMs]] (scaffolded).
+
+**Festival** — common shorthand for a curated multi-restaurant
+context. Not an entity stored in this extension; see
+[[webapp-integration]].
+
+**Internal payment** — an LNbits invoice paid from another wallet
+on the same instance, never touching the Lightning Network. The
+extension supports this as `payment_method = "internal"` for testing
+and same-instance flows.
+
+**MAX_MENU_DEPTH** — `3` (zero-indexed); 4 levels of nesting total.
+Soft-enforced by the API via HTTP 400 on creates / moves.
+
+**msat** — millisatoshi. Money on `orders` and `order_items` is
+stored as integer msat for precision; UI / Nostr surfaces convert
+back to sat (or fiat) at display time.
+
+**Node** — a row in `menu_nodes`. The unit of organization in the
+[[menu-tree]]. Has zero or more children, zero or more items, and
+zero or one parent.
+
+**NIP-XX** — a Nostr Implementation Possibility. Reference repo at
+`~/dev/nostr-protocol/nips`. Specific NIPs we use:
+
+- **NIP-01** — base event structure; kind 0 metadata.
+- **NIP-09** — deletion request (kind 5).
+- **NIP-17** — gift-wrapped DMs (kind 1059); planned order intake.
+- **NIP-44** — encryption used inside NIP-17.
+- **NIP-51** — generic lists; festival aggregator vehicle.
+- **NIP-99** — classified listings (kind 30402); how we publish menu items.
+
+**Operator** — the LNbits user who has enabled this extension on
+their account. Owns one or more restaurants.
+
+**Parent order ref** — an opaque string on `orders.parent_order_ref`
+the webapp can use to correlate its own umbrella-cart id with the
+per-restaurant orders. The extension stores it and echoes it back;
+never reads it.
+
+**Path** — denormalized materialized path on `menu_nodes`. Either
+`'rootid'` (for a root node) or `'rootid/childid/...'` (for deeper
+nodes). Underpins [[menu-tree|cheap subtree queries]].
+
+**Restaurant Nostr identity** — each restaurant has an effective
+keypair for signing kind-0 / kind-30402 events. If
+`restaurant.nostr_pubkey` is set it overrides; otherwise the LNbits
+Account keypair of the wallet owner is used. See [[nostr-layer]].
+
+**Slug** — the URL segment under which a restaurant's [[cms|CMS pages]]
+live (e.g. `/restaurant/emporium`). Lowercase, dashes, no spaces.
+
+**Webapp** — the customer-facing UI at `~/dev/webapp`. Subscribes
+to restaurants over Nostr, posts orders over REST. See
+[[webapp-integration]].