feat(voyageai): refresh model-name constants to current Voyage models

[fzowl]

What & why

Refreshes the convenience model-name constants for the three VoyageAI
Weaviate modules to match the models currently offered by Voyage AI, verified
against the official docs (embeddings, reranker, contextualized-chunk, pricing
pages on docs.voyageai.com).

Module	Added (current)	Kept (legacy)
text2vec-voyageai	voyage-4-large, voyage-4, voyage-4-lite, voyage-code-4, voyage-finance-2, voyage-law-2, voyage-context-4	voyage-3-large, voyage-3.5, voyage-3.5-lite, voyage-3, voyage-3-lite, voyage-context-3
reranker-voyageai	rerank-3, rerank-3-lite, rerank-2.5, rerank-2.5-lite	rerank-2, rerank-2-lite, rerank-1, rerank-lite-1
multi2vec-voyageai	voyage-multimodal-3.5, voyage-multimodal-3 (this class had no constants before)	—

Non-breaking: every pre-existing constant is retained (grouped as legacy);
the constants are only helpers — any model string can still be passed directly.

Scope notes (campaign tasks 1–4)

This repo is a client that configures Weaviate's server-side *-voyageai
modules via JSON schema — it never calls Voyage's embedding API itself. That
determined what was in scope:

1. Open-PR review — the fork (fzowl) has no open PRs. Upstream
   weaviate/java-client has 7 open PRs; the only one from a fork
   (cross-repository) is feat(collections): create from and read raw schema JSON weaviate/java-client#598 — "feat(collections): create from and read raw
   schema JSON" by @dudanogueira, state OPEN, mergeable. The other six are
   internal branches (fix(tenants): split tenant updates at the server's limit of 100 weaviate/java-client#616, fix(collections): nest the quantizer inside a dynamic index weaviate/java-client#613, fix(quantizers): use the field names the server actually reads weaviate/java-client#612, fix(rerankers): send the Nvidia reranker base URL as "baseURL" weaviate/java-client#610, fix: serialise OffsetDateTime as RFC 3339 weaviate/java-client#609, fix(query): allow rerank on every search operator weaviate/java-client#608).
2. "VoyageAI by MongoDB" rebrand — not applied. There is no README/docs/UI
   prose that names VoyageAI in this repo. Every occurrence is an API identifier
   (class names, enum values, the server module strings text2vec-voyageai /
   multi2vec-voyageai / reranker-voyageai, method names) or a javadoc
   reference to those Weaviate modules. Renaming them would break the wire
   contract and users' source; injecting marketing text into Weaviate's javadoc
   isn't appropriate here. The task's "where relevant" qualifier resolves to
   nothing in this client.
3. Model-list update — this PR (verified against docs.voyageai.com).
4. contextualized_embed inputs: Union[List[List[str]], List[str]] — not
   applicable. That is the Python voyageai SDK's API. This Java client has no
   embedding-call surface at all; it only sets model=voyage-context-4 on the
   text2vec-voyageai config and the Weaviate server performs the embedding
   calls. voyage-context-4 is now exposed as a constant.

Validation

No JDK/Maven is available in this environment, so the change was not compiled
locally. It is additive-only (new public static String/final String fields,
no new imports or logic), so risk is minimal; CI on this PR will validate the
build.

[fzowl]

VERDICT:APPROVED

Reviewed the diff (3 files, +25/-2) and commit hygiene.

Correctness — Purely additive. New public static String model-name constants for the three VoyageAI modules, no logic/imports/wire changes. The model strings match the PR table and Voyage's documented naming (voyage-4-large/-4/-4-lite, voyage-code-4, voyage-finance-2, voyage-law-2, voyage-context-4; rerank-3/-3-lite/-2.5/-2.5-lite; voyage-multimodal-3.5/-3). The reranker reordering only moves RERANK_1/RERANK_LITE_1 down — values unchanged.

Conventions — Follows each file's existing style: the new reranker constants keep public static final String (consistent with that file), and the vectorizer constants match that file's public static String pattern and formatting. Added javadoc-style comments with official docs.voyageai.com links, which is an improvement over the previously bare constants.

Breaking-change risk — None. Every pre-existing constant is retained (grouped as "legacy"), so it's source- and wire-compatible. Constants are convenience helpers; arbitrary model strings can still be passed.

Tests / docs — No tests, which is appropriate: these are literal string constants with no behavior to exercise, matching the existing (untested) constants. No README/prose changes needed — the rebrand and contextualized_embed inputs tasks are correctly assessed as N/A for a client that only configures Weaviate's server-side modules.

Hygiene — Single commit authored by fzowl zoltan@voyageai.com, no trailers, no Co-Authored-By / "Generated with" text, no .claude/ files. Clean.

Minor nit (non-blocking, pre-existing): the vectorizer constants are non-final public static String, so they're technically reassignable; the new ones inherit that pattern. Worth tightening to final file-wide someday, but out of scope here. Not compiled locally (no JDK/Maven), but the additive-only nature makes that low-risk and CI will confirm.

LGTM.