Implement update_tasks mutation flow

[deverman]

Summary:

• implement update_tasks in the shared mutation pipeline from Add Shared Mutation Core for CLI and MCP #29
• expose the new operation through CLI and MCP
• add task patch validation and tests for the v1 homogeneous-bulk contract

Validation:

• node --check Plugin/FocusRelayBridge.omnijs/Resources/BridgeLibrary.js
• swift test
• swift run focusrelay bridge-health-check
• swift run focusrelay list-tasks --fields id,name --limit 1
• swift run focusrelay update-tasks --name Preview Only Rename --preview-only --verify --return-fields id,name,flagged

Notes:

• this PR is intentionally stacked on Add shared mutation core preview pipeline #40 and should not merge before Add shared mutation core preview pipeline #40
• live validation used --preview-only to avoid mutating real OmniFocus data on this machine
• OmniAutomationService.performMutation now reuses the bridge-backed mutation path for update_tasks so v1 task updates have one execution implementation

[deverman]

Merge-order note: this PR is intentionally stacked on #40 and should not merge before #40 lands. After #40 merges, retarget or rebase this branch onto master before final review/merge.

[deverman]

Behavior note from live validation: renaming did not move the test task. The structural side effect appeared after the tag add/remove test on an inbox item. OmniFocus can automatically clean up tagged inbox items into a default single-action project depending on the user Organization preference named Clean up inbox items which have. On this machine that resulted in the task leaving Inbox and appearing under Personal single actions, with the project-level Mac Computer tag then visible in the task payload and UI. This is an OmniFocus-side cleanup effect that should be documented for inbox tag mutations. It is not a rename-specific mutation bug in update_tasks.

[deverman]

Merge-order note: the follow-up work for issue #31 is being stacked on top of this PR because task completion reuses the CLI and MCP mutation surfaces introduced here. Merge #41 before the future #31 PR.