kernel: the word interner (Registration) moves out of busbar-contract

[MattJackson]

CONTRACT-ABI lane, item 3 (part 1 of the contract statics): the word interner moves into the kernel.

THE DESIGN A.8 "Statelessness" (docs/design/BUSBAR-1.6.0.md l.3701): busbar-contract has no static, OnceLock, LazyLock or thread_local outside tests (gate contract-stateless). C.2 (l.3893): Contract statics (codec.rs, records.rs:94, ids.rs:330): deleted, with host tables used instead. This PR covers the ids.rs:330 row.

• crates/busbar-kernel/src/vocabulary.rs (new) holds Registration, MAX_VOCABULARY and the image's VOCABULARY/FROZEN, moved verbatim from busbar-contract/src/ids.rs:312-479. Only the docs changed: they reasoned about a dynamically loaded plugin reaching the interner through its own copy of the contract. A plugin's closure is the contract alone (Part 2 deps: bump schemars from 1.2.1 to 1.2.2 #40(a)), and the contract no longer holds the interner, so the docs now say that. busbar_kernel::{Registration, MAX_VOCABULARY} are re-exported at the crate root.
• busbar-contract loses the type, the statics and their lib.rs re-exports. The caps/egress.rs doc link (in a deny(broken_intra_doc_links) module) becomes prose.
• Callers: the composition root (root/kernel.rs, plane_node.rs, durability/mod.rs, tests/kernel.rs) and busbar-llm (engine/build_runtime.rs, engine/tables.rs, unit tests) now name busbar_kernel::Registration. In the plane crates a2a/llm/streaming, the docs name the host's interner in prose, because a plane names no kernel crate. busbar-plane-decisions is left untouched: four open PRs delete it (P5 rulings: base layer lays pinned transports; linked-dropped-features and plugin-closure-deps read pinned plugins (stacked on #894, #901) #935/plane-delete-test: a pinned plane is deleted by its pin and feature (stacked on #888) #894/P5: busbar-plane-decisions leaves for its own repo, pinned (/status rows 106/107; stacked on #838) #888/busbar-contract: YAML readers behind a yaml feature, enabled by busbar-kernel #897). Its doc link is only a rustdoc warning and goes with the file.
• qa/contract-stateless.toml strikes the three ids.rs rows this drains (LazyLock, FROZEN, VOCABULARY): 44 → 41. The drain-only ledger turns a reintroduced contract interner red.

RED: the interner's tests move with it to crates/busbar-kernel/tests/vocabulary_{cap,freeze,resolve}.rs (git renames). The boot_cells.rs interning test becomes vocabulary_intern.rs. Each names busbar_kernel::Registration, so none compiles on predev. Each stays its own test binary because the vocabulary is the process's.

Lane TODO note: item 5, "ed25519-dalek → ring", is struck (coordinator ruling 2026-10-14). The ARCHITECT 2026-10-02 refusal stands (deny.toml:90-97).

Shared files (rule 20): git merge-tree is clean against every non-draft open PR touching these files: #981, #944, #941, #935, #927, #913, #904, #897, #894, #888, #863, #862, #817, #805, #804 and #503.

No dependency change. No behaviour change: the same interner, ceiling and freeze, in the host.

[MattJackson]

#1028 also edits qa/contract-stateless.toml: it strikes the two codec.rs contract-stateless:static rows (ENTROPY_SOURCE, WALL_CLOCK). Different rows; adjacent-row conflict settles by hand (rule 13).

[MattJackson]

Rule 20 note from #1030 (row 155): qa/contract-stateless.toml, disjoint rows struck (services.rs OnceLock/KEPT/FILLING, codec.rs USAGE_TAP_FAULT_LATCH/REPORTER). A test merge is clean.