fix: revert oapi to v2.6.0 (#209)

<!-- CURSOR_SUMMARY -->
> [!NOTE]
> **Medium Risk**
> Regenerates large portions of `lib/oapi/oapi.go`, including request
parameter encoding and server parameter binding helpers, which could
subtly change runtime behavior. Main risk is mismatched query/path
parsing or validation differences after the codegen upgrade.
> 
> **Overview**
> Regenerates `lib/oapi/oapi.go` with `oapi-codegen` v2.6.0, updating
the embedded swagger payload, adding `Valid()` helpers for multiple
enums, and switching generated request/handler parameter styling/binding
to the newer `runtime.*WithOptions` APIs (with explicit `Type`/`Format`,
e.g. UUIDs and booleans).
> 
> Simplifies the `oapi-generate` Makefile target by dropping the
`patch_strict_optional_json` step and deletes
`scripts/oapi/patch_strict_optional_json`, leaving only the SSE methods
patch as a post-processing step.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
e270add. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: archandatta

server/Makefile

@@ -24,8 +24,6 @@ oapi-generate: $(OAPI_CODEGEN)
 	$(OAPI_CODEGEN) -config ./oapi-codegen.yaml ./openapi-3.0.yaml
 	@echo "Fixing oapi-codegen issue https://github.com/oapi-codegen/oapi-codegen/issues/1764..."
 	go run ./scripts/oapi/patch_sse_methods -file ./lib/oapi/oapi.go -expected-replacements 3
-	@echo "Patching strict JSON optional bodies (io.EOF) + response omitempty tags..."
-	go run ./scripts/oapi/patch_strict_optional_json -file ./lib/oapi/oapi.go
 	go fmt ./lib/oapi/oapi.go
 	go mod tidy