feat(ogar-vocab): class_ids module — canonical home for codebook constants

[AdaWorldAPI]

What

Promotes the compile-time pub const u16 class-id constants from the two -rs consumer crates (redmine-canon::class_ids, op-canon::class_ids) into ogar-vocab itself. The CODEBOOK lives here, so the named constants that vouch for it live here too.

Why

The two consumer crates have ended up with byte-identical class_ids modules (same 26 project-mgmt + 6 commerce constants, same drift-guard tests). That's a smell — the codebook is a single artifact minted once in OGAR, and the constants are its typed face. They shouldn't be re-declared in every consumer.

This PR makes ogar-vocab the canonical home. Follow-on PRs on each port will swap their local class_ids.rs for pub use ogar_vocab::class_ids; (re-export), so the two ports stop duplicating the same numbers and instead inherit OGAR's drift guards.

New surface (additive)

• pub mod class_ids with one pub const u16 per promoted concept (26 project-mgmt + 6 commerce = 32 constants).
• class_ids::ALL: &[(&str, u16)] — every (name, id) pair the constants vouch for, for tabular dispatch / debug.

Drift guards

• constants_match_codebook (forward gate) — every entry in ALL agrees with canonical_concept_id(name) for the same name.
• every_codebook_entry_has_a_const (reverse gate) — if CODEBOOK promotes a new concept, ALL must learn it (catches "promotion landed without exposing a const").
• constants_are_unique_and_non_zero.
• divergent_curator_names_share_one_constant — pins the headline pairs (a Redmine Issue and an OpenProject WorkPackage both route on PROJECT_WORK_ITEM).

Tests

ogar-vocab unit tests 46 → 50 (+4 class_ids tests); cargo check --workspace --all-targets + cargo test --workspace green.

Follow-ons

Two thin PRs on the -rs ports to replace the local class_ids.rs with a re-export from ogar_vocab::class_ids. No surface change for downstream consumers.