# Proposal comments: wire the existing is_deleted field end-to-end

Child of musehub#141 (parent: framework-wide CRUD/delete idiom).

## Background

`MusehubProposalComment` (`musehub/db/musehub_social_models.py:344-390`)
already has an `is_deleted` column — but nothing uses it. `muse hub
proposal comment` only has `list` and `create` subcommands; there is no
delete endpoint, no CLI command. Compare to `MusehubIssueComment`, which
has the identical field *and* a fully wired `muse hub issue
comment-delete` command.

Confirmed hitting this directly during #139's cleanup: 7 test comments
added to a real proposal for layout verification cannot be removed.

## Goal

- Add the delete endpoint (soft-delete, sets `is_deleted`) mirroring
  whatever `issues.py`'s comment-delete route does today.
- `muse hub proposal comment delete <proposal-id> --comment-id <id>` —
  soft-deletes by default, matching #141's framework-wide idiom.
- `--hard` flag for actual row removal, same guard/authorization pattern
  as the issues child ticket (#142) and #141's parent idiom.
- Soft-deleted comments excluded from `comment list` by default (same
  `--include-deleted` convention as #142, for consistency).

## Out of scope

- Any change to issue comments' existing delete path — it already works
  and is the reference implementation for this ticket, not something to
  touch.