Implement `update_tasks` for Homogeneous Bulk Field Patches

[deverman]

Summary

Implement update_tasks / focusrelay update-tasks for homogeneous bulk task field patches.

One request applies one patch set to many task IDs.

Scope

Supported v1 task patches:

• name
• note replace
• note append
• flagged
• estimatedMinutes
• dueDate set/clear
• deferDate set/clear
• tag add
• tag remove
• tag set
• tag clear

Out of scope:

• completion state changes
• moves/reparenting
• planned date writes (tracked separately in Feature Request: Write Support for OmniFocus Planned Date field [Future] #16)
• mixed per-item patch payloads
• name-based task lookup

Public Behavior

• input is a list of task IDs plus one shared patch
• default output is compact summary data
• returnFields can request selected post-write fields
• previewOnly validates and resolves without mutating
• verify reads back and confirms the final state

Acceptance Criteria

• same patch applies to all provided task IDs
• invalid IDs fail deterministically
• clear-date behavior is explicit and tested
• tag operations are deterministic and documented
• CLI and MCP use the same mutation path and output model

Test Plan

• success cases for each supported patch type
• invalid ID handling
• preview-only behavior
• verify readback behavior
• homogeneous bulk update across multiple task IDs

Notes

Keep completion and move semantics out of this tool.

[deverman]

Execution/merge-order note: issue #30 is intentionally stacked on PR #40 because update_tasks should build on the shared mutation core rather than creating a separate write path. Merge PR #40 before merging the future PR for this issue.

[deverman]

Implementation is now in draft PR #41. Merge-order reminder: PR #41 remains intentionally stacked on #40 and should be reviewed/merged only after #40 lands.