fix(assistant): pass workspace to life pulse rhythm

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Summary

• Fixes a desktop Life Pulse bug where rhythm first checked the active workspace for due scheduled jobs, then spawned skilllite schedule tick without forwarding that workspace.
• In packaged desktop contexts, the subprocess cwd is not reliably the project workspace, so due schedule jobs could be skipped even after Life Pulse detected them as due.
• The fix mirrors the existing growth argument-helper pattern and passes --workspace <active workspace> to the rhythm subprocess, with a focused unit test for the argument shape.

Task Linkage

• Task ID: TASK-2026-070
• Task folder: tasks/TASK-2026-070-life-pulse-rhythm-workspace/

Injected Specs

• spec/architecture-boundaries.md (if architecture/layering changed)
• spec/security-nonnegotiables.md (if sandbox/security changed)
• spec/testing-policy.md (required for any code change)
• spec/docs-sync.md (if behavior/docs/env/commands changed)

Validation Evidence

• Commands executed:
  • cargo fmt --check && python3 scripts/validate_tasks.py
  • rustup update stable && rustup default stable
  • sudo apt-get update && sudo apt-get install -y libgtk-3-dev libsoup-3.0-dev libwebkit2gtk-4.1-dev libayatana-appindicator3-dev librsvg2-dev
  • cd crates/skilllite-assistant && npm ci && npm run build
  • cargo test --manifest-path crates/skilllite-assistant/src-tauri/Cargo.toml life_pulse::tests
  • cargo test
  • cargo clippy --manifest-path crates/skilllite-assistant/src-tauri/Cargo.toml --all-targets -- -D warnings
  • cargo clippy --all-targets -- -D warnings
• Key results:
  • Task validation passed: Task validation passed (70 task directories checked).
  • Focused Life Pulse tests passed: 2 passed; 0 failed; 52 filtered out.
  • Workspace cargo test passed with exit code 0.
  • Clippy checks were executed but failed on pre-existing warnings/lints outside this patch: assistant dead-code warnings / existing sort_by suggestions and crates/skilllite-core/src/config/schema.rs:313 manual_filter under Rust 1.97.

Regression Scope

• Areas likely affected:
  • crates/skilllite-assistant/src-tauri/src/life_pulse.rs
  • Desktop Life Pulse rhythm-triggered schedule execution.
• Explicit non-goals:
  • CLI schedule tick semantics or flags.
  • Evolution growth scheduling behavior.
  • Repository-wide Rust 1.97 clippy cleanup.

Docs Sync (EN/ZH)

• Not needed
• Updated EN + ZH docs
• Files:
  • N/A; no documented command, flag, env var, or user-facing default changed. Desktop now calls the existing CLI flag correctly.

Review Checklist

• Acceptance criteria in tasks/TASK-2026-070-life-pulse-rhythm-workspace/TASK.md satisfied (or explicitly deferred)
• tasks/TASK-2026-070-life-pulse-rhythm-workspace/STATUS.md updated with latest progress
• tasks/TASK-2026-070-life-pulse-rhythm-workspace/REVIEW.md includes merge readiness decision
• tasks/board.md status is up to date