feat: separate internal schema dimensions from embedding API request dimensions

[jszhang98]

PR Title

feat: separate internal schema dimensions from embedding API request dimensions

Summary

This PR decouples two previously conflated dimension semantics in the embedding pipeline:

• Internal dimensions used for LanceDB schema sizing and local vector validation.
• Request dimensions sent to embedding providers that support variable output dimensions.

After this change:

• embedding.dimensions is treated as internal schema/validation dimension.
• embedding.requestDimensions is optional and only used for API request payload fields.
• If requestDimensions is not configured, no dimensions field is sent to embedding APIs by default.
• omitDimensions=true still has highest priority and suppresses dimensions fields even when requestDimensions is set.

Motivation

Some providers/models (for example non-matryoshka-compatible models) reject dimensions/output_dimension in request payloads.

Previously, embedding.dimensions was reused for both storage and API request parameters, which could cause provider-side 400 errors during startup/runtime.

This PR keeps storage behavior stable while preventing accidental request-parameter injection.

What Changed

• Embedding config model extended with requestDimensions.
• Embedder request payload dimension source changed from dimensions to requestDimensions.
• Plugin config parsing and wiring updated to pass requestDimensions explicitly.
• Plugin schema updated to declare embedding.requestDimensions.
• Regression tests updated to reflect new default behavior and precedence rules.

Behavior Matrix

• dimensions only:
  • Used internally for schema/validation.
  • Not forwarded to embedding API payload.
• requestDimensions set:
  • Forwarded as provider-specific request field (dimensions/output_dimension).
• requestDimensions + omitDimensions=true:
  • Request dimension fields are omitted.

Backward Compatibility

• Existing storage behavior remains unchanged.
• Existing users relying on implicit forwarding of embedding.dimensions to API payload should migrate to embedding.requestDimensions.
• No change to fixed-dimension LanceDB table constraints in this PR.

Files Updated

• src/embedder.ts
• index.ts
• openclaw.plugin.json
• test/plugin-manifest-regression.mjs

Testing

• Updated regression assertions for new dimension-forwarding semantics.
• Added schema assertion for embedding.requestDimensions.
• Local full test command was blocked in current environment due missing jiti package dependency, but modified regression logic and assertions are in place.