feat(search): semantic image search with CLIP embeddings

[dschmidt]

Semantic image search: semantic:"dog on a beach" finds images by content, no tags needed, any language the model covers.

Indexing: a ClipExtractor decorator (around basic/tika) embeds images via a CLIP inference service (immich machine-learning API). Querying: the clause text is embedded into the same space and images are ranked by cosine similarity, bleve via faiss KNN behind the new vectors build tag, OpenSearch via knn_vector. The clause is split off the parsed KQL tree and composes with the rest of the query: the filter part scopes the neighbor search and owns the totals, hybrid rankings fuse via RRF, purely semantic queries return just the ranking. Vector size is index schema (512, startup probe hard-fails on mismatch); in bleve the raw vector lives in a stored-only sibling field so it survives move/delete/restore.

Enable with SEARCH_EXTRACTOR_CLIP_URL; bleve needs a build with ENABLE_VECTORS=true (faiss stage in Dockerfile.multiarch); existing content needs a force reindex.

Open: configurable dims/model, originals vs thumbnails to the service, capability flag for clients, web search bar wraps input as name:"*...*", OR/NOT position degrades to AND, faiss release/CI story, immich-ml is AGPL (external unmodified service).

[codacy-production]

Not up to standards ⛔

🔴 Issues 1 critical

Alerts:
⚠ 1 issue (≤ 0 issues of at least minor severity)

Results:
1 new issue

Category	Results
Security	1 critical

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🟢 Metrics 148 complexity

Metric	Results
Complexity	148

View in Codacy

🟢 Coverage 42.28% diff coverage · +0.18% coverage variation

Metric	Results
Coverage variation	✅ +0.18% coverage variation (-1.00%)
Diff coverage	✅ 42.28% diff coverage

View coverage diff in Codacy

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (993265b)	88137	20641	23.42%
Head commit (4993c9c)	88669 (+532)	20929 (+288)	23.60% (+0.18%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#3316)	570	241	42.28%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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