docs: centralize issue sop

[PerishCode]

Why

The PerishCode issue handling loop is now a shared perish.top operating SOP, not
a flavor product rule. Keeping the full implementation/reporter cadence in
this repository would duplicate the global ~/.codex/AGENTS.md instructions
and invite drift across repos.

What

• Replace the duplicated issue hot follow-up flow with a pointer to the global
  PerishCode issue SOP.
• Keep only the flavor-specific command mapping:
  • no-install validation commands
  • runseal :release
  • runseal :pr
  • manage.sh / manage.ps1 local CLI updates
• Remove duplicated GitHub tool auth guidance from the repo file now that it is
  maintained globally.

Tests

• git diff --check
• cargo fmt --all --check
• cargo clippy --locked --workspace --all-targets -- -D warnings
• cargo test --locked --workspace
• cargo run --locked -p flavor-cli -- check --root . --config flavor.toml
• Commit hook:
  • cargo fmt
  • cargo check
  • flavor self-check
  • shell syntax checks
  • Python syntax checks
  • PowerShell syntax checks