workstation-v0: autopatch shell rc + fish support + CI smoke tests

[mdheller]

Implements a productivity upgrade: optional, idempotent shell rc autopatching + palette actions.

Changes:

• profiles/linux-dev/workstation-v0/bin/patch-shell.sh:
  • idempotently patches bash/zsh rc files with a bounded marker block
  • fixes correctness: avoids baking the current PATH into the rc file at patch time
  • adds CI/test hook SOURCEOS_RC_FILES (colon-separated list) to enable idempotency testing
• profiles/linux-dev/workstation-v0/bin/patch-fish.sh:
  • idempotently patches fish config ($XDG_CONFIG_HOME/fish/config.fish) to source the fish spine
• profiles/linux-dev/workstation-v0/shell/common.fish:
  • fish-native spine (fish_add_path, direnv, atuin, zoxide, ergonomic aliases)
• profiles/linux-dev/workstation-v0/bin/sourceos:
  • adds sourceos fix shell [apply|dry-run] and palette entries
• profiles/linux-dev/workstation-v0/install.sh:
  • optional autopatch via SOURCEOS_AUTOPATCH_SHELL=1
  • when enabled, also patches fish config (if present)
• docs/workstation/RUNBOOK.md:
  • documents autopatch option and fish lane
• CI hardening (in this PR branch):
  • adds a patch-shell idempotency smoke test using a temp rc file

Why:

• This eliminates the manual "edit rc files" step while keeping it opt-in and auditable.

Safety:

• Uses marker blocks; will not duplicate changes.
• Default is non-invasive; autopatch must be enabled.