feat(buzz-cli, buzz-sdk): add buzz projects command group (NIP-MP kind:30621 write path)

[wpfleger96]

Implements the buzz projects command group — the NIP-MP Phase 2 write path. The relay accepted kind:30621 in #3171; this delivers the Rust builder (required by the NIP-MP conformance obligation) and the seven CLI commands that make projects writable from the CLI.

What this adds

crates/buzz-sdk/src/builders.rs — two-layer builder

Layer A (protocol):

• validate_project_envelope(tags, content) — enforces the 8 NIP-MP ingest rules: d-cardinality, d-empty/length, member-tag-arity (2–3 elements), member-cap (64 raw a tags before dedup), member-coordinate grammar (first-two-colons split, literal 30617, lowercase 64-hex owner, non-empty remainder), member-duplicate (by coordinate only), singleton metadata cardinality, and byte bounds (name 256 / description 2048 / buzz-channel 256 / buzz-visibility 256).
• build_project_with_tags(content, tags) — raw Layer A builder; no canonicalization; accepts every valid fixture envelope including opaque metadata, non-empty content, relay hints, and unknown tags.
• ProjectMemberCoord — 30617:<owner-hex>:<repo-d> + optional opaque relay hint; equality/Hash by coordinate only.

Layer B (writer policy):

• build_project(slug, name, description, members, channel, visibility) — constructs the single d tag, enforces UUID channel and listed|unlisted visibility, emits empty content; composes onto Layer A.

Shared:

• build_delete_addressable(kind, pubkey, d) — generic NIP-09 kind:5 coordinate delete. build_workflow_delete now delegates to this.
• All 31 NIP-MP.fixtures.json cases exercised directly through build_project_with_tags; accepts build, rejects fail tied to the named rule; count assertion guards against omissions.

crates/buzz-cli/ — seven commands

buzz projects create <slug> --repo <coord> [--name] [--description] [--channel <uuid>] [--visibility listed|unlisted]
buzz projects get <slug> [--owner <pubkey>]
buzz projects list [--owner <pubkey>] [--limit <n>]
buzz projects add-repo <slug> --repo <coord> [--repo <coord>]...
buzz projects remove-repo <slug> --repo <coord> [--repo <coord>]...
buzz projects update <slug> [--name|--clear-name] [--description|--clear-description] [--channel <uuid>|--clear-channel] [--visibility listed|unlisted|--clear-visibility]
buzz projects delete <slug>

Command semantics:

• create: collision-guarded preflight — returns Conflict if the slug already exists; requires ≥1 --repo.
• update: at least one setter/clearer required (runtime guard before any network I/O); omission preserves; --clear-* drops the tag; setter + clearer are mutually exclusive per clap group.
• delete: head-based tombstone at created_at = head + 1; post-submit re-query verifies tombstone landed; returns Conflict if a concurrently newer head survived.
• All mutations: strip auth, re-validate full envelope through Layer A before publish; created_at advances from observed head, never wall-clock.
• --repo bare form (Buzz repo-id [a-zA-Z0-9._-]{1,64}) auto-expands with caller's pubkey; full 30617:<owner-hex>:<repo-d> for cross-owner or colon-bearing IDs.
• Relay hints on existing member tags are preserved verbatim through RMW.
• remove-repo of an absent coordinate returns NotFound.

Shared infrastructure:

• commands/mod.rs: parse_write_response() extracted from repos.rs; adopted by repos.rs (thin wrapper) and projects.rs directly.

Limitations (recorded, not in scope)

• No relay-hint authoring: --repo carries a coordinate only; existing hinted a tags survive RMW unchanged. Authoring syntax deferred until there's a demonstrated need.
• Signer-self delete only: the relay's NIP-OA owner-delete extension is not exposed; delete targets the signer's own coordinate.
• Deletion durability: the watermark carry-over from the relay layer applies; delete is best-effort against a later-arriving replacement.

Live round-trip

Blocked pending relay deployment of #3171 to production (kind:30621 currently rejected at wss://buzz.block.builderlab.xyz with "unknown event kind"). Local Docker relay is also not available in the current environment. The round-trip will be run and the transcript posted to the thread as soon as either path is available.