docs(modularization): D10 spec amendment — back-align §G D10.e cursor error codes to §C.3 canonical (#1710)

Per [D10 spec amendment] thread (Bryce msg=441c5e56 + PM msg=40e98684 +
architect 双签):

§G D10.e Deliverable summary (line 1115) had 6 SCREAMING_SNAKE codes that
did not match §C.3 body's 6 snake_case codes. The §G summary was a drafting
slip from the rushed §G decomposition amendment commit (36b5835); §C.3 body
remains the canonical source because:

  1. Casing — wire format is snake_case to match the rest of the ApeRAG API
     surface (existing error codes use snake_case in JSON wire format).

  2. Granularity — §C.3 body splits invariant violation into 3 distinct
     codes (cursor_filter_mismatch / cursor_tenant_mismatch /
     cursor_index_changed) because line 567-571 maps DIFFERENT client
     recovery paths to each:
       - cursor_filter_mismatch  → client bug, surface to user
       - cursor_tenant_mismatch  → security violation, distinct telemetry
       - cursor_index_changed    → backend ops issue, retry from null
     Collapsing them into a single cursor_invariant_mismatch would lose
     this distinction and force clients to over-react.

  3. CURSOR_FOREIGN and CURSOR_PAGE_OUT_OF_RANGE in §G summary did not
     appear in §C.3 body and had no client-recovery path defined — they
     were drafting noise, not real codes.

§G D10.e summary now cites §C.3 verbatim and points readers at the §C.3
body for the client-recovery mapping (single source of truth).

Doc-only change. No implementation impact. Unblocks task #97 (D10.e
cursor errors.py).

Co-authored-by: 符炫炜 <fuxuanwei@apecloud.io>

Author: earayu

docs/modularization/d10-design-pack.md

@@ -1112,7 +1112,7 @@ Lane-to-§ mapping is one-to-one with the design pack so reviewers can locate sp
 
 #### D10.e — Pagination + cursor contract (§C)
 
-- **Deliverable**: opaque base64 cursor + `invariant_hash` field + 6 explicit error codes (`CURSOR_EXPIRED` / `CURSOR_INVARIANT_MISMATCH` / `CURSOR_MALFORMED` / `CURSOR_FOREIGN` / `CURSOR_PAGE_OUT_OF_RANGE` / `CURSOR_VERSION_MISMATCH`); cursor is **never silently reset** — explicit error always.
+- **Deliverable**: opaque base64 cursor + `invariant_hash` field + 6 explicit error codes per §C.3 canonical (`cursor_invalid` / `cursor_expired` / `cursor_filter_mismatch` / `cursor_tenant_mismatch` / `cursor_index_changed` / `cursor_schema_unsupported`); cursor is **never silently reset** — explicit error always. Wire-format casing is **snake_case** to match the rest of the API surface; client-recovery path mapping is in §C.3 body (line 567-571), not duplicated here.
 - **Owner candidate**: @Bryce (canonical caller-migration discipline from #90 round-4 fix-forward; pagination semantics are caller-sensitive) — fallback @cuiwenbo.
 - **Write-set boundary**:
   - `aperag/mcp/cursor/codec.py` + `cursor/invariants.py` + `cursor/errors.py` (new package)