feat(studio): add GitHub CI/CD delivery for Studio-generated agents

[CatherineKu]

Adds a GitHub-backed continuous delivery path for Studio-generated Agent
projects. Instead of pushing images directly, Studio can now open (or update)
a pull request in the user's GitHub repo carrying the generated Agent source,
and bind that pipeline to an AgentKit Runtime.

The existing veadk pipeline command assumes a specific Volcengine account
and region (hardcoded CR instance name, VPC tunnel region, and template image),
so it is not portable across accounts. This PR introduces a GitHub-PR-centric
flow driven only by a repo URL + token, keeping delivery in the user's own
repository and CI.

Changes

Backend

• New veadk github-cicd-pipeline CLI command
  (veadk/cli/cli_github_cicd_pipeline.py): takes --github-url,
  --github-branch, --github-token, --project-json, --region.
• New orchestration module veadk/cli/github_cicd.py:
  • Parses GitHub HTTPS/SSH URLs, validates repo access.
  • Creates/reuses a studio/<agent> branch, commits the project files,
    and creates or updates the PR.
  • Runtime binding + config re-sync (bind / sync), with pipeline state
    persisted under ~/.veadk/github-cicd-pipelines.json.
  • Credentials are redacted from all error/log output.
• New Studio APIs in veadk/cli/cli_frontend.py:
  • POST /web/github-cicd/pipelines
  • GET/POST /web/github-cicd/runtime-binding
  • POST /web/github-cicd/runtime-sync

Frontend

• New GithubCicdPanel in Studio project preview, with API client wrappers.
• Rebuilt static assets under veadk/webui/.

Tests

• Backend tests: tests/cli/test_github_cicd.py
• Frontend test: frontend/tests/githubCicdPanel.test.mjs

Notes

• Guardrails on project payload: max 800 files, 2 MB/file, 25 MB total.
• The frontend build output (veadk/webui/) is committed separately as a
  chore commit.

How to test

veadk github-cicd-pipeline \
  --github-url https://github.com/<owner>/<repo> \
  --github-branch main \
  --github-token <token> \
  --project-json ./project.json