fix: prevent duplicate tasks from :TwAdd

[MattHandzel]

Summary

• request UUID-oriented output from task add with rc.verbose=new-uuid
• distinguish Taskwarrior command success from UUID extraction success
• never retry a parsed add merely because its successful output lacks a UUID
• retain the raw fallback only when capture parsing itself cannot run
• add an end-to-end regression that drives the real :TwAdd command and <CR> callback

Root cause

Taskwarrior normally reports a numeric working-set ID (Created task 1.), while tw_add only recognized permanent UUIDs. The first task add succeeded, but UUID extraction returned an empty string. Capture treated that as a failed mutation and ran a second raw task add, creating a duplicate.

The fix makes normal output deterministic using Taskwarrior's automation-oriented new-uuid verbosity token. It also treats mutation success and output parsing as separate facts: if the command succeeds but no UUID can be extracted, capture warns and does not retry.

User impact

:TwAdd creates one task across default and quiet Taskwarrior verbosity settings. Parsed fields such as due: and project: remain attached to that single task. Ambiguous successful output no longer causes either a duplicate or a false "add failed" message.

Validation

• ./tests/e2e/run.sh capture_relative_dates_spec.lua — 5 passed
• ./tests/lua/bootstrap.sh — all Lua tests passed
• tests were run from a detached worktree containing only commit 4223246

Fixes #7