Wire CLI to core: teach/do/pack/doctor call real engine functions

[SuperInstance]

Summary

Wires the four target stub commands (teach, do, pack, doctor) in pincher-cli to real pincher-core functions. Also wires status, shellinfo, and reflexes while at it.

Changes

pincher teach

• Changed from a standalone stub to Commands::Teach { intent: String, action: String }
• Calls ReflexEngine::teach(&intent, &action)? — persists the reflex to SQLite with embeddings
• Output: [TAUGHT] reflex <id> — intent: "...", action: "..."

pincher do

• Calls ReflexEngine::do_command(&input)? — matches intent against stored reflexes
• Supports Exact, Similar, and Novel match types
• Output: match type, confidence, latency, matched reflex ID, execution output

pincher pack

• Calls pincher_core::migration::pack_nail(&db_path, &output)? — creates real .nail (tar.zst) archives
• Includes reflexes.db, identity.json, config.toml, manifest.json with BLAKE3 checksums

pincher doctor

• Real health checks: SQLite connectivity, embedder status (ONNX/fallback), bwrap availability, disk space, hardware fingerprint, binary integrity
• Green/red output with details

Also wired

• status: calls ReflexEngine::get_status() for live counts
• shellinfo: calls fingerprint() for real hardware fingerprinting
• reflexes: lists all reflexes from the database via get_all_reflexes()
• Added expand_tilde() for ~/.pincher/... db path support

Verification

• cargo test -p pincher-core: 130 tests pass
• pincher teach successfully stores reflexes
• pincher do matches and executes stored reflexes
• pincher pack creates valid zstd-compressed .nail archives
• pincher doctor runs 6 real health checks
• cargo check -p pincher-cli: clean, no warnings

[SuperInstance]

Superseded by PR #6 which wires all 13 commands. Keeping the wiring pattern for reference.