chore(actions): replace deployment PAT with app dispatch

[risu729]

Summary

Use the shared deployment-dispatch-action in .github/workflows/docker.yml instead of directly checking out and editing csesoc/deployment from this repo's workflow, and split qa from ptb by publishing to distinct image names.

Changes

• replace the current deploy step flow with devsoc-unsw/deployment-dispatch-action@main
• switch GHCR publish authentication to github.token
• publish projects-bot to ghcr.io/csesoc/projects-discord-bot
• publish develop to ghcr.io/csesoc/projects-discord-bot-qa
• dispatch the branch-specific image name instead of a shared image name
• use vars.DEPLOYMENT_DISPATCHER_APP_ID and secrets.DEPLOYMENT_DISPATCHER_APP_PRIVATE_KEY

Context

This supersedes the earlier dispatch-only PR for develop because csesoc/deployment matches manifests by image name. Without distinct image names, dispatch updates would hit both qa and ptb.

Dependencies

• csesoc/deployment PR: https://github.com/csesoc/deployment/pull/3873

Verification

• rg -n "\\bGH_TOKEN\\b|IMAGE_NAME|projects-discord-bot-qa" . -S -g '!node_modules'
• actionlint -color .github/workflows/docker.yml still reports the same pre-existing baseline issues for old Docker action refs and the missing steps.meta definition

[risu729]

Superseded by #227, which is rebuilt directly from instead of from an earlier PR branch.

[risu729]

Superseded by #227, which is rebuilt directly from develop instead of from an earlier PR branch.