[M3] mxaccess-galaxy: GalaxyUserProfile + UserResolver trait + role-blob

Lands the user-resolver half of M3 stream A. Pure-Rust foundation —
the tiberius-backed SQL impl is logged as F14 and stays gated behind
the existing galaxy-resolver Cargo feature.

New
- role_blob.rs (~270 LoC, 12 tests including a garbage-between-roles
  edge case) — port of ParseRoleBlob (cs:87-133). Sliding-window scan
  over hex-decoded UTF-16LE bytes; rejects non-printable code units;
  case-insensitive dedup. Pure function, no I/O.
- user.rs (~290 LoC, 8 tests including 4 tokio-driven InMemoryUserResolver
  cases) — GalaxyUserProfile (port of cs:5-11) + from_columns helper
  bridging into role_blob + UserResolver async trait + UserResolverError
  with NotFound / Backend variants.
- sql.rs additions: USER_SELECT_SQL + USER_BY_GUID_SQL + USER_BY_NAME_SQL
  constants (port of cs:135-148). Inline concatcp! macro composes the
  base SELECT with each WHERE clause at compile time without pulling
  const_format.

Cargo.toml: added uuid (Galaxy user_guid is a uniqueidentifier).

design/followups.md: added F14 (P2) for the tiberius-backed SQL impl
behind the galaxy-resolver feature.

Test count delta: 427 -> 446 (+19; mxaccess-galaxy 30 -> 49). All four
DoD gates green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

rust/crates/mxaccess-galaxy/src/lib.rs

@@ -29,8 +29,12 @@
 pub mod metadata;
 pub mod parser;
 pub mod resolver;
+pub mod role_blob;
 pub mod sql;
+pub mod user;
 
 pub use metadata::GalaxyTagMetadata;
 pub use parser::{ParseError, ParsedTagReference};
 pub use resolver::{Resolver, ResolverError};
+pub use role_blob::parse_role_blob;
+pub use user::{GalaxyUserProfile, UserResolver, UserResolverError};