Drop Protobuf; move continuum/v1 domain model to JSON Schema

Nothing imported the proto-generated code (zero references to
continuum-rust-types or @continuum/ts-types's proto export in any
consumer repo), and protobuf's real value - one schema compiled to a
compact binary wire format for both languages - never applied: BE<->proxy
and FE<->BE are both JSON. Also fixes 8 broken $ref paths in the bambulab
schemas and a root tsconfig.json that was sweeping the gitignored
examples/ directory into typecheck.

- proto/continuum/v1/*.proto -> schemas/continuum/v1/*.schema.json
- packages/rust-types: hand-written serde structs instead of
  prost-build codegen
- packages/ts-types: drop the generated/ proto barrel export, keep the
  hand-written TypeBox schemas as the TS source of truth
- root package.json: drop build:ts, protoc, ts-proto

package.json

@@ -6,13 +6,11 @@
     "packages/*"
   ],
   "scripts": {
-    "build:ts": "protoc --plugin=protoc-gen-ts_proto=./node_modules/.bin/protoc-gen-ts_proto --ts_proto_out=packages/ts-types/src/generated --ts_proto_opt=esModuleInterop=true,outputServices=false,useOptionals=messages,outputIndex=true -I proto $(find proto -name '*.proto')",
     "build:rust": "cargo build -p continuum-rust-types --manifest-path packages/rust-types/Cargo.toml",
-    "build": "npm run build:ts && npm run build:rust",
+    "build": "npm run build:rust",
     "typecheck": "tsc -b"
   },
   "devDependencies": {
-    "ts-proto": "^1.181.0",
     "typescript": "^5.5.0"
   }
 }