[plan] Remove gojsonschema dependency from go.mod

[github-actions]

Objective

Remove the unmaintained github.com/xeipuuv/gojsonschema dependency from the project after successfully migrating to santhosh-tekuri/jsonschema.

Context

After migrating campaign validation to use santhosh-tekuri/jsonschema, the gojsonschema library is no longer used anywhere in the codebase and should be removed.

Prerequisites

• [plan] Migrate campaign validation from gojsonschema to santhosh-tekuri/jsonschema #6402 must be completed (campaign validation migrated)
• All tests must be passing

Implementation Steps

1. Verify no usages remain:

   grep -r "gojsonschema" . --include="*.go"

   Should return no results in .go files (may appear in discussion/spec files which is fine)

2. Remove from go.mod:

   go mod tidy

   This will automatically remove unused dependencies

3. Verify removal:

   grep "xeipuuv/gojsonschema" go.mod go.sum

   Should return no results

4. Run full test suite:

   make test

5. Verify binary size reduction (optional):

   make build
   ls -lh gh-aw

Files to Modify

• go.mod (automatic via go mod tidy)
• go.sum (automatic via go mod tidy)

Acceptance Criteria

• github.com/xeipuuv/gojsonschema not present in go.mod
• No references to gojsonschema in any .go files
• go mod tidy completes successfully
• All tests pass (make test)
• Code builds successfully (make build)
  Related to [plan] Migrate from unmaintained gojsonschema to santhosh-tekuri/jsonschema #6401

AI generated by Plan Command for discussion #6400