feat: blocklist display + introspection — *KB Sharing* Blocked view (closes #162)

[cuttlefisch]

What

PR 3 of 3 for #162 (ADR-039 A2 local blocklist) — closes the issue. PR1 (#186, merged) = daemon enforcement; PR2 (#187) = human+AI action surface. This adds the display + introspection: a *KB Sharing* Blocked section, at-point unblock, and the blocked principals surfaced in kb_sharing_status / (kb-sharing-status).

Why a fetch (not the local replica)

Membership renders from the editor's local kbc: replica — but the blocklist is local-only on the daemon and never in the synced collection (that's the design). So the editor can't derive it; it must fetch the authoritative state. An optimistic local mirror would miss blocks set in a prior session or by another frontend on a shared daemon.

Daemon

• DocStore::all_kb_blocklists() + a read-only kb/blocklist query RPC → { blocklist: { kb_id: [fp, …] } } (optional kb_id scopes to one). This is the ONLY way a client learns the local-only blocklist.

Editor

• CollabState.kb_blocklists cache; a send_blocklist_fetch helper sent on connect (durable prior-session blocks) and after each block/unblock (the user's own changes); reply → PendingResponseKind::Blocklist → CollabEvent::BlocklistUpdated → cache + repaint. Display-only; the daemon stays authoritative.
• KbSharingEntry.blocked: Vec<BlockedView> in build_snapshot (label resolved best-effort from the member replica; a non-member block falls back to the short fingerprint).
• *KB Sharing* buffer: a foldable Blocked (N) section after Pending; at-point B → unblock (kb-sharing-unblock, not owner-gated); diagnostic.error theme key.
• Introspection: because all three actors share build_snapshot, the blocked list flows automatically into the kb_sharing_status MCP tool and (kb-sharing-status) Scheme primitive (CLAUDE.md chore(deps): Update crossterm requirement from 0.28 to 0.29 #3/ci(deps): Bump the ci-dependencies group with 2 updates #8).

Tests

• Daemon: extends the block-fence test with the kb/blocklist query oracle (reports exactly the blocked principal).
• Editor: blocklist_renders_blocked_view_with_member_label — bob stays a member (a local block is not a removal) and is listed Blocked with his label; a non-member block has an empty label; the buffer view emits a BlockedHeader + one Blocked row per principal.

Verification

• Daemon: 120 lib + 51 handler tests, clippy clean.
• Editor: fmt --check + clippy --workspace --all-targets -D warnings clean (incl GUI); cargo test --workspace green.

Closes #162.

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