Add a repo-local archive for retired whys and decouple notes from park

[fuzzyporpoise]

Summary

Adds .todo/archive/, a repo-local home for retired whys, and decouples todo's note contract from park/schema. A completed task is retired with todo archive, which asserts the note's one-line relevance why and moves it into the repo where the work happened, so a how-did-we-fix-this search lands in the right place and relevance is inherited from the repo.

What's new

• Archive command - todo archive <ref> retires a completed [x] task: it asserts the note's synopsis (existing, or --synopsis), rewrites the note as a todo-native record, writes .todo/archive/<ID>.md (--name overrides the basename), and removes the task line and the source note entry.
• Archived view - todo list --archive prints a compact NAME/SYNOPSIS view of the archive; --json emits a versioned {schema_version, archived[]} envelope; --all aggregates across registered repos. Default list never shows archived content.
• Native note contract - todo defines its own durable note shape (kind: record plus created/source/synopsis) and no longer imports github.com/polymorcodeus/park/schema. add -n without a disposition flag now stamps a native record.
• Park interop kept - --category still emits a park-shaped record, rendered locally and byte-compatible with park's WriteTemplate, and NoteDisposition still recognizes a park note by the bare category: key.
• Recorded disposition in clear - a completed task whose note is a native record has its line removed but the note preserved, reported separately from parked notes.

Usage

Command	Purpose
todo archive <ref> [--synopsis ...] [--name ...]	retire a done task into .todo/archive/
todo list --archive [--all] [--json]	compact view of archived notes

Behavior changes / guardrails

• archive only accepts a completed [x] task with a companion note; a failed guard mutates nothing.
• The synopsis is a gate: an empty result is an error, never a silently unlabeled archive entry. The note's existing synopsis pre-fills it and --synopsis overrides it.
• The archive directory is created and populated in the same pass, because the lnk store prunes empty directories.
• Writes are repo-side only: todo stays lnk-agnostic and store adoption is out of band. The source note entry is unlinked (symlink only), so an adopted note's store copy is left for the lnk step.
• NoteDisposition precedence is kind: work-order > category: (park) > kind: record > float.
• add -n default output changes from a park record (category: areas) to a native record (kind: record); existing park-shaped notes keep working through category:.

Testing

• Unit tests cover the native and park note shapes, NoteDisposition, the archive happy path, the synopsis gate, the done/note guards, synopsis override plus --name, ListArchived sorting and the missing-directory case, and clear preserving record notes.
• CLI tests cover archive, list --archive, list --archive --json, and the error path when a work-order note is archived without a synopsis.
• make check runs fmt, vet, lint, and tests; all green.