Fix project context resolution for file-based commands

[techmannih]

Why

File-based commands were resolving runtime project context from process.cwd() instead of the target file path.

That meant tsci export and tsci simulate analog could load the wrong tscircuit.config.* and resolve the wrong user-land dependencies when they were run from outside the target project directory.

Before

• export loaded runtime config from the shell working directory
• simulate analog loaded runtime config from the shell working directory
• shared user-land module resolution also depended on the shell working directory
• the same file could produce different results depending on where the command was launched from

After

• file-based commands derive project context from the target file path
• the CLI finds the nearest tscircuit.config.ts, tscircuit.config.js, or tscircuit.config.json starting from the target file directory
• user-land module resolution now follows the target project context instead of the shell working directory
• export and simulate analog now behave consistently when invoked with absolute or nested file paths from outside the target project directory

What Changed

• added nearest-config lookup in the project config loader
• updated export to resolve runtime config from the target file path
• updated simulate analog to use the same project resolution behavior
• updated shared user-land module resolution to resolve from the target project directory
• added @tscircuit/ti-parts-engine to package.json
• updated bun.lock for the new dependency
• added a regression test covering file-based export from outside the target project

Validation

• bun test tests/cli/runtime-project-config-command-flows.test.ts
• bun test tests/lib/project-config.test.ts
• bun test tests/cli/export/export-circuit-json.test.ts tests/cli/export/export-kicad-library.test.ts tests/cli/simulate/simulate.test.ts