feat(desktop): GA token quick-access via subscription portal

- Add pq-ga-token button (shown when portal available)

- Bridge GET/POST /subscription-portal -> agentmain.start_subscription_portal

- i18n zh/en; bump app.js/i18n cache versions

- llmcore: maxlen_multiplier factor 0.85->0.75

Merge pull request #679 from shenhao-stu/fix/update-prompt-overlay-merge

fix(slash_cmds): merge additive-overlay files (e.g. .gitignore) on /update

fix: limit parallel max_workers to 3

feat: generic extra_sys_prompts slot replaces hardcoded commit_signat…

…ure module

feat: add Tauri desktop shell + desktop_bridge (url mode, no-console)

refactor: unified mykeys dict, support mykey.py and mykey.json dual f…

…ormat