fix(agent-manager): resolve spaced argv0 in AGENTS matchers

[codeaholicguy]

Summary

• Reuse executablePath() in matchArgv0, matchArgv0Name, and matchAnyBasename.
• Detect agents whose executable is installed beneath a path containing spaces.
• Avoid filesystem checks unless the command is a plausible spaced-path candidate.
• Prevent words inside the installation directory from being treated as executable matches.

Closes #297

Validation

• Includes regression coverage for spaced executable paths and false-positive directory tokens.

Follow-up

• matchAnyToken intentionally continues scanning arguments for cases such as Gemini launched as a Node script.