Merge branch 'main' into ragnorc/omnigraph-mcp-crate

Folds in v0.7.2 (release #301) + RFC-013 Phase 7 (graph lineage in __manifest,
internal schema v3→v4 migration #299; WriteTxn #298; recovery convergence #296)
under the MCP branch.

Conflict resolutions (2 files):
- crates/omnigraph-server/Cargo.toml: take main's 0.7.2 path-dep constraints;
  keep our omnigraph-mcp dep (bumped to 0.7.2).
- docs/releases/v0.8.0.md (add/add): both branches drafted v0.8.0 notes for the
  same next minor — combined them. v0.8.0 now documents BOTH the MCP surface
  (ours) and main's __manifest lineage fold + the breaking internal-schema-v4
  upgrade-order requirement (kept prominent under Upgrade notes). Corrected our
  'no breaking changes / on-disk format unchanged' line, which the v4 migration
  makes false.

Coherence: omnigraph-mcp [package] + Cargo.lock bumped 0.7.1→0.7.2; openapi.json
auto-merged to info.version 0.7.2 (no API-surface drift from the incoming
engine-internal commits). Verification deferred to CI (no local rebuild).

openapi.json

@@ -7,7 +7,7 @@
       "name": "MIT",
       "identifier": "MIT"
     },
-    "version": "0.7.1"
+    "version": "0.7.2"
   },
   "paths": {
     "/graphs": {