feat: add --no-expand flag to qmd query

[kechol]

#454

Summary

Add a --no-expand flag to qmd query that skips LLM query expansion and searches the original query verbatim.

Motivation

The built-in query expansion model (qmd-query-expansion-1.7B) is trained primarily on English. Given a non-English query — Chinese, Japanese, Korean — it translates the query into English before generating lex/vec/hyde variants. The vector search downstream then runs against English-translated text, and on a non-English corpus recall drops sharply.

A typed-query path ({ type: 'lex', query: ... } via SDK or MCP) bypasses expansion already, but for the simple ergonomic qmd query "..." CLI path there was no escape hatch. This PR adds one.

Changes

• qmd query --no-expand skips expansion entirely and searches the original query verbatim. Mirrors --no-rerank.
• SDK: search({ query, expand: false }) — analogous to the existing rerank: false.
• HybridQueryOptions.skipExpansion plumbs through to hybridQuery(). When set, expandQuery() is not called and the lex/vec/hyde fan-out is empty — only the original query runs against BM25 and the vector index.
• CLI hook output emits a single Expansion disabled (--no-expand) line on stderr so users see the flag took effect, instead of the misleading "Expanding query..." line.
• MCP query tool already takes pre-expanded searches, so expansion is structurally absent there. No MCP changes needed.

Usage

# Skip expansion for non-English queries
qmd query "テレグラム 設定" --no-expand

# Same effect via SDK
const results = await store.search({ query: "テレグラム 設定", expand: false })

Notes

• Default behavior is unchanged when --no-expand is absent (or expand is unset / true).
• Strong-BM25-signal short-circuit still works on the default path; --no-expand just makes the bypass unconditional.
• Pairs naturally with --no-rerank for the lowest-latency CPU path: qmd query "..." --no-expand --no-rerank runs only BM25 + vector + RRF, no LLM calls.