feat: canonical POST /load, deprecate /ingest (RFC-009 Phase 5) (#222)

* feat(server): canonical POST /load, deprecate /ingest (RFC-009 Phase 5)

The CLI's non-deprecated `load` verb rode the deprecated `/ingest` route, so
`/ingest`'s eventual removal would silently break it. Add a canonical `/load`,
mirroring the shipped `/mutate`↔`/change` and `/query`↔`/read` pattern.

- Extract `server_ingest`'s body into a shared `run_ingest` (branch-exists /
  fork-if-`from`, Cedar auth, admission, `load_as`, `IngestOutput` mapping).
- `server_load` (canonical) → `run_ingest`, `Json<IngestOutput>`.
- `server_ingest` (deprecated) → `run_ingest` + `#[deprecated]` + RFC 9745/8288
  `Deprecation: true` / `Link: </load>; rel="successor-version"` headers.
- Router mounts `/load` (same 32 MB body limit) beside `/ingest`; OpenAPI
  `paths(...)` gains `server_load` and flags `server_ingest` deprecated.

`/load` reuses `IngestRequest`/`IngestOutput`, exactly as canonical `/mutate`
reuses `Change*` — a DTO rename is a separate, larger change (out of scope).

openapi.json regenerated. Tests: openapi `/load` present + not deprecated,
`/ingest` deprecated, `/load` bearer-secured; data_routes `/load` happy path +
`/ingest` deprecation headers. Existing `/ingest` route tests stay green (the
shim is unchanged). Docs: server.md endpoint table; RFC-009 Phase 5 marked
landed (incl. the hand-mount-vs-utoipa-axum registration finding).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* feat(cli): point remote load at /load (RFC-009 Phase 5)

`GraphClient::load`'s remote arm now POSTs to the canonical `/load` route
instead of the deprecated `/ingest`; the deprecated `ingest` verb keeps
riding `/ingest`. `parity_load` exercises `/load` on the remote arm (its
documented flip); the matrix exclusions comment is updated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

docs/user/server.md

@@ -56,7 +56,8 @@ Per-graph endpoints — same body shape across modes; URLs differ:
 | POST | `/queries/{name}` | `/graphs/{id}/queries/{name}` | bearer + `invoke_query` (+ `change` for a stored mutation) | invoke a named query from the `queries:` registry; deny == 404 | `server_invoke_query` |
 | GET | `/schema` | `/graphs/{id}/schema` | bearer + `read` | get current `.pg` source | `server_schema_get` |
 | POST | `/schema/apply` | `/graphs/{id}/schema/apply` | bearer + `schema_apply` (target=`main`) | migrate | `server_schema_apply` |
-| POST | `/ingest` | `/graphs/{id}/ingest` | bearer + `branch_create` (only when `from` is set and the branch is created) + `change` | bulk load; branch creation is opt-in via `from` — without it a missing `branch` is a 404, never an implicit fork | `server_ingest` (32 MB body limit) |
+| POST | `/load` | `/graphs/{id}/load` | bearer + `branch_create` (only when `from` is set and the branch is created) + `change` | bulk load (canonical); branch creation is opt-in via `from` — without it a missing `branch` is a 404, never an implicit fork | `server_load` (32 MB body limit) |
+| POST | `/ingest` | `/graphs/{id}/ingest` | bearer + `branch_create` (only when `from` is set and the branch is created) + `change` | **deprecated** alias of `/load` (carries `Deprecation: true` + `Link: </load>; rel="successor-version"`) | `server_ingest` (32 MB body limit) |
 | GET | `/branches` | `/graphs/{id}/branches` | bearer + `read` | list branches | `server_branch_list` |
 | POST | `/branches` | `/graphs/{id}/branches` | bearer + `branch_create` | create | `server_branch_create` |
 | DELETE | `/branches/{branch}` | `/graphs/{id}/branches/{branch}` | bearer + `branch_delete` | delete | `server_branch_delete` |