refactor(authn): one Principal.CanRead() for the read-plane ACL (spec-ejq.1)

graph's gate, web's mayRead and mcpsrv's Gate each hand-spelled
'IsOwner() || IsAgent()' — three copies of the read ACL, which graph's own
comment warned is how a corpus leaks when they drift. Define it once as
authn.Principal.CanRead and route all three through it.

coreauth.Derive keeps its own owner||agent test on purpose: it answers a
different question (is this an owner-backed identity to bridge to
AUTH_INTERNAL), and coupling it to the read ACL would misroute a future
read-only viewer kind to the owner's UserID.

Closes spec-ejq.1

feat(webhooks): fire on proposal open/merge/reject (Phase 5a)

The firing half — proposal lifecycle events now deliver GraphQL-native
webhooks. Verified end to end against a live daemon: an agent REST
propose delivers a signed POST whose body is the subscription's stored
query executed against the ProposalEvent payload.

- service: an EventSink seam (service/events.go). Propose emits
  PROPOSAL_OPENED for a new proposal, mergeProposal emits PROPOSAL_MERGED
  (the single merge point — both auto-merge and the human approve reach
  it), Reject emits PROPOSAL_REJECTED. Nil-safe; a Service with no sink
  emits nothing.
- graph.NewProposalEvent builds the *model.ProposalEvent payload from a
  service.Proposal (reusing the existing service→graph→model mapping).
- cmd webhookEventSink: proposal events happen in the service layer,
  which has none of core-go's request context, so the sink enqueues a
  dowork task onto the webhook queue. The task runs in the queue's worker
  context (server+database+config, from WithQueues), adds the owner's
  INTERNAL auth, and calls Schedule — which renders each subscriber's
  query and delivers it Ed25519-signed. Fire-and-forget off the write
  path: a webhook never blocks or fails a proposal write.

Phase 5a (webhooks) is complete: DB, the authn→AuthContext bridge, the
GraphQL surface, the core-go server wiring, and firing.

feat(cmd,graph): wire /query onto core-go's server for webhooks (Phase 5a)

The faithful runtime wiring. /query moves from spec's anon-router handler
onto core-go's authenticated router, so the webhook engine gets the
auth/database/server context it requires.

- cmd: build the executable schema via graph.NewSchema and hand it to
  both webhooks.NewQueue and server.WithSchema (one schema, both). The
  server is coreserver.New().WithDefaultMiddleware() (core-go auth +
  database + server context + the delivery worker via WithQueues). web,
  MCP and REST stay on the anon router with spec's own authn — only
  /query changes. The owner "user" row is seeded at startup so core-go's
  LookupUser stays local.
- ownerOnly middleware on /query: 403s any non-owner (core-go auth admits
  any meta user; spec is single-owner) and remaps the owner to
  AUTH_INTERNAL so the webhook engine's NewAuthConfig/FilterWebhooks
  (which refuse AUTH_COOKIE) accept them.
- graph: NewSchema exposes the raw executable schema; the webhook
  resolver ACL now requires AUTH_INTERNAL (only the owner gets it, via
  ownerOnly) instead of spec's authn, which is no longer in the /query
  chain.

Accepted trade-off: agents lose GraphQL /query reads (they keep MCP +
REST). New deploy requirement: WithDefaultMiddleware needs [mail]
smtp-from (core-go's notification queue).

Verified against a live daemon on Postgres: owner cookie creates and
lists webhooks (row stored INTERNAL/user_id 1); non-owner 403; unauth
401; web UI 200 on the anon router.

feat(graph): GraphQL-native webhook surface (Phase 5a)

The webhook types, mutations, and resolvers, adapted from the pages.sr.ht
core-go template for spec's single-owner model.

- SDL: WebhookEvent (PROPOSAL_OPENED/MERGED/REJECTED), WebhookSubscription
  interface + UserWebhookSubscription, WebhookDelivery, WebhookPayload
  interface + ProposalEvent (carries a Proposal), cursor wrappers,
  `webhook` payload root field, and a `type Mutation` with
  createUserWebhook / deleteUserWebhook. No OAuth `client` field and no
  @access/@private directives — spec has no OAuth clients or scopes, so
  the owner gate is the entire ACL.
- Models: hand-written database.Model impls (UserWebhookSubscription,
  WebhookDelivery) so gqlgen autobinds rather than generates them; events
  via pq.Array; cursor keyset pagination.
- Resolvers: all owner-gated via authn (spec's ACL), using core-go's
  webhook engine — Validate, NewAuthConfig (INTERNAL, via the coreauth
  bridge), FilterWebhooks, WebhookContext.Exec for the sample, and the
  `webhook`→Payload(ctx) root. Proposal writes deliberately stay off this
  surface (only webhook mutations; the schema test now asserts exactly
  that).
- gqlgen.yml binds Cursor to core-go's model.Cursor; generated code
  regenerated with the pinned gqlgen v0.17.36 (reproducible).

Compiles and vets clean; existing graph read tests still pass. Runtime
context wiring and event firing are the next slices.

feat(graph): wire the proposals read to service.ListProposals (Phase 3)

The Proposals port declared a proposal listing and left Options.Proposals
nil, so the `proposals` query failed loudly with "service/ exposes no
proposal listing yet". Phase 3 supplies it: an adapter maps
service.Proposal onto graph.Proposal at the edge — the two structs are
identical, but service/ must not import graph/, so the rename lives here
beside web.NewReader's equivalent — and cmd wires graph.NewProposals(svc)
into the schema. The `proposals` field now answers from service/.

feat(graph): the read-only GraphQL schema at /query

Eight query fields over the service layer, no Mutation and no
Subscription — the design defers mutations until the proposal state
machine settles, and TestSchemaHasNoMutations stands guard on that.

Access is fail-closed and gated before parse, matching web's ACL exactly,
so introspection is treated as content too. A federating api.sr.ht must
therefore present a token or skip us, which costs one log line.

A malformed rev is reported as a GraphQL error rather than folded into
null. service/ deliberately hides malformed-versus-absent from probing,
but the caller here is already authenticated as the owner or its own
agent, and a bare null for rev=proposals/42 is indistinguishable from an
absent document — it reads as a silently dropped argument.

Proposal listing declares its port but is unwired: service/ exposes no
proposal read yet, and returning an empty list would tell a reviewer their
queue is clear when it is merely unread.