Fix desktop evolution workspace split-brain for nested workspaces

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Summary

• Fixes a critical desktop evolution split-brain bug where chat/A9 canonicalized a nested workspace to the parent project root, but evolution UI subprocesses passed the raw nested path to CLI --workspace.
• Adds a shared canonical workspace argument helper and applies it to desktop evolution status/backlog/proposal/pending/confirm/reject/authorize/manual run paths plus Life Pulse growth runs.
• Adds nested workspace regression tests for assistant path canonicalization, evolution UI argument construction, authorize follow-up run args, and Life Pulse growth args.

Task Linkage

• Task ID: TASK-2026-070
• Task folder: tasks/TASK-2026-070-desktop-evolution-workspace-canonicalization/

Injected Specs

• spec/architecture-boundaries.md (desktop bridge boundary preserved)
• spec/security-nonnegotiables.md (not applicable)
• spec/testing-policy.md (Rust code change)
• spec/docs-sync.md (checked; user docs not needed because no command/env/docs surface changed)

Validation Evidence

• Commands executed:
  • cargo fmt
  • cargo test --manifest-path crates/skilllite-assistant/src-tauri/Cargo.toml
  • cargo fmt --check
  • cargo clippy --all-targets -- -D warnings
  • cargo test
  • cargo clippy --manifest-path crates/skilllite-assistant/src-tauri/Cargo.toml --all-targets -- -D warnings
  • python3 scripts/validate_tasks.py
• Key results:
  • Assistant tests passed: 55 passed; 0 failed.
  • Root cargo fmt --check, root cargo clippy --all-targets -- -D warnings, root cargo test, and task validation passed.
  • Assistant-specific clippy is blocked by existing unused/dead-code warnings in the excluded Tauri crate; failures do not point to the new canonical workspace helper or updated evolution UI call sites.

Regression Scope

• Areas likely affected:
  • Desktop assistant evolution UI subprocess --workspace arguments.
  • Life Pulse evolution growth subprocess arguments.
• Explicit non-goals:
  • CLI-only evolution reset / disable / explain workspace flag design.
  • Sandbox behavior, Python SDK behavior, and broad workspace discovery refactors.

Docs Sync (EN/ZH)

• Not needed
• Updated EN + ZH docs
• Files:
  • N/A

Review Checklist

• Acceptance criteria in tasks/TASK-2026-070-desktop-evolution-workspace-canonicalization/TASK.md satisfied.
• tasks/TASK-2026-070-desktop-evolution-workspace-canonicalization/STATUS.md updated with latest progress.
• tasks/TASK-2026-070-desktop-evolution-workspace-canonicalization/REVIEW.md includes merge readiness decision.
• tasks/board.md status is up to date.