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>

crates/omnigraph-cli/src/client.rs

@@ -304,10 +304,13 @@ impl GraphClient {
                 token,
             } => {
                 let data = std::fs::read_to_string(data)?;
+                // RFC-009 Phase 5: the canonical `load` verb targets the
+                // canonical `/load` route (the deprecated `ingest` verb below
+                // still rides `/ingest`).
                 let output = remote_json::<IngestOutput>(
                     http,
                     Method::POST,
-                    remote_url(base_url, "/ingest"),
+                    remote_url(base_url, "/load"),
                     Some(serde_json::to_value(IngestRequest {
                         branch: Some(branch.to_string()),
                         from: from.map(ToOwned::to_owned),