feat(skills): add semantic-search skill

Expose the local Qwen search as a skill with an explicit trigger for concept
questions, the command for both shells, result handling, and its limits.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

shared/skills/research/semantic-search/SKILL.md

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+---
+name: semantic-search
+description: Use when you must find where a behavior, concept, or rule lives in a repository and do not know its identifiers or exact strings, or when a first rg search returned nothing useful. Returns ranked code and documentation chunks from the local Qwen index.
+---
+
+# Semantic Search
+
+Search the current Git repository by meaning with the locally installed Qwen3 embedding and reranking models.
+
+## When to use
+
+- Concept questions: "where are expired trials blocked", "how is the cache invalidated", "which code retries failed uploads".
+- Unfamiliar repositories where names and conventions are unknown.
+- After an `rg` search for guessed terms returned nothing relevant or too many unrelated files.
+
+Use `rg` or direct reads instead for known file paths, symbol names, exact strings, and error messages.
+
+## Run
+
+PowerShell:
+
+```powershell
+python "$HOME/.my-ai-configuration/semantic-retrieval/server.py" search --root . --data-dir "$HOME/.my-ai-configuration/semantic-retrieval/data" --model-cache "$HOME/.my-ai-configuration/semantic-retrieval/model-cache" --query "<question in natural language>" --top-k 5
+```
+
+Bash:
+
+```bash
+python3 "$HOME/.my-ai-configuration/semantic-retrieval/server.py" search --root . --data-dir "$HOME/.my-ai-configuration/semantic-retrieval/data" --model-cache "$HOME/.my-ai-configuration/semantic-retrieval/model-cache" --query "<question in natural language>" --top-k 5
+```
+
+The output is a JSON list of `{path, symbol, text, score}`, best match first.
+
+## Use the results
+
+1. Phrase the query as a full question about behavior, not as a keyword list.
+2. Open the top hits and verify them against the current files before acting; the index can lag behind uncommitted edits by one refresh.
+3. Follow the verified hit with `rg` for its symbols to find callers and tests.
+
+## Cost and limits
+
+- The first search in a repository builds its index, which can take minutes; later searches refresh only changed files.
+- Outside a sandbox a background daemon keeps the models loaded, so warm searches take seconds. Inside the Codex sandbox every search loads the models again and takes about half a minute; batch related questions into one precise query.
+- Only Git-tracked and unignored files up to 512 KB are indexed, by default at most 2000 files per repository.
+- If the command fails or the setup is missing, continue with `rg` and state the limitation briefly.