fix: insert intake at the top of ## Items, not at EOF

[hkwuks]

Summary

hooks/task intake wrote every new entry at end-of-file. When ## Removed was the last section, the new live entry landed in the deleted region — outside ## Items and inside the range todo-check reads for authorized deletions — and it contradicted the documented convention at the top of todo.md (<!-- Add new items at the top using the template below. -->).

Insertion is now an index, not EOF: after ## Items (skipping blanks and its leading HTML comment), else just before ## Removed, else the old EOF path for bare fixtures. Goal/ID duplicate checks and the field template are unchanged; the block goes through the shared emit() path.

TaskFlow traceability

• Task: TaskFlowDocs/2026-09-22-todo-intake-insert/
• Todo item: TF-20260921-337ab8
• Scope: hooks/task (intake branch only), hooks/smoke-test (new section), task documents, TaskFlowDocs/todo.md status bookkeeping
• Base branch: main
• Target repository: hkwuks/TaskFlow (origin)

Verification

• bash hooks/smoke-test — ALL SMOKE PASSED
• git diff --check — clean
• Relevant Skill/plugin validation — quick_validate.py skills/taskflow → Skill is valid!; no skill file is touched by this PR
• Results recorded in the TaskFlow Plan — TaskFlowDocs/2026-09-22-todo-intake-insert/plan.md, ## Verification / Review

Beyond the suite: bash -n hooks/task and bash -n hooks/smoke-test clean; four manual fixtures (Items+trailing Removed, bare # Todo, no Items+Removed, Removed-above-first-entry) confirmed order Items < new < seed < Removed and that the new ID is absent from the removed_at range.

Review boundaries

• No secrets or opaque remote payloads included
• No unrelated task or user files changed — only the intake insertion path, its smoke section, and this task's documents/status
• Remote/base assumptions are stated — pushed to origin (hkwuks/TaskFlow), targeting main
• Known limitations and follow-ups are documented below

Known limitations

• Promote still derives the task directory from the section heading. Titles that do not match Goal are unchanged (deferred; PRD Open Question 1).
• A todo.md with ## Removed but no ## Items is malformed relative to the documented layout; intake inserts before ## Removed and does not refuse (PRD Open Question 2 / R2).
• The EOF path for a bare # Todo file is intentionally unchanged so existing minimal smoke fixtures stay valid (R3).