Add Bash script support

[Omar-Elwazeery]

Summary

Fixes #1203.

• Register Bash/shell as a supported Tree-sitter language using the existing WASM grammar pipeline.
• Add Bash detection for .sh, .bash, .bats, and extensionless scripts with Bash/POSIX shell shebangs.
• Add a Bash extractor for shell functions, assignments, exported/readonly variables, command calls, and static source/script imports.
• Include extensionless Bash shebang scripts in scan/sync flows and add Bash import resolution for shell/Bats files.
• Add regression coverage for detection, extraction, scanning, sync, and .bats import resolution.

Testing

• ✅ npm test -- __tests__/extraction.test.ts __tests__/resolution.test.ts __tests__/sync.test.ts -t Bash
• ✅ npm run build
• ⚠️ npm test currently times out in the full-suite parallel run at __tests__/mcp-daemon.test.ts > proxy survives the daemon dying mid-session and keeps serving (#662). I confirmed the same full-suite timeout occurs on a clean base after stashing this branch, and the exact test passes when run isolated both before and after this change.