docs(wrap-it-up): add inbox sanity check + checklist line

Wrap-up never knew about the inbox. After process-inbox.org landed
today as the formal workflow for handoff intake, wrap-it-up.org
needs to surface inbox/ when it's non-empty so the wrap doesn't
silently defer handoffs to next session.

This commit adds a new Inbox sanity check sub-step under Step 3
(project hygiene). The check runs find inbox -maxdepth 1 -type f
filtered to skip .gitkeep and PROCESSED-* prefixes. A non-zero
count surfaces with the file list and a recommendation to run
process-inbox.org or explicitly defer each item. A zero count or no
inbox/ directory makes the check a silent no-op.

It also adds one line to the Validation Checklist: inbox is empty
(excluding .gitkeep and PROCESSED-* prefixes), OR each remaining
item has an explicit deferral logged in the valediction.

This is the only integration gap surfaced today. The other gaps
considered (LAST_INBOX_PROCESS marker stamp, sync-check, make
status) didn't justify wrap-up changes. The marker is
process-inbox's own responsibility. sync-check is project-specific
to rulesets. make status doesn't generalize across projects.

0 files changed, 0 insertions, 0 deletions