CLI polish: make restore path handling explicit

[jonathanpopham]

Summary

During v0.6.14 production surface verification, supermodel restore --local --dir /definitely/missing correctly failed with a missing-directory error.

One polish issue surfaced: supermodel restore --local /some/path silently ignores the positional argument because the command only reads the --dir flag and does not validate args. The command docs/examples use --dir, so this is not blocking, but it is easy to misread from a CLI-user perspective.

Proposed fix

Pick one behavior and test it:

• Prefer: accept an optional positional path (restore [path]) and map it to the same behavior as --dir.
• Alternative: set Args: cobra.NoArgs so unexpected positional args fail fast.

Verification context

• Release: v0.6.14
• Happy path verified: restore . --local --max-tokens 1000
• Reverse path verified: restore --local --dir /definitely/missing exits non-zero

[coderabbitai]

🔗 Related PRs

#18 - feat: add supermodel restore command [merged]
#56 - Add supermodel share command [merged]
#73 - Allow compact, clean, status, hook, restore to run without an API key [merged]
#84 - fix(restore): fall back to directory walk when worktree has uncommitted changes [merged]
#109 - fix: rootCmd args parsed as directory path — breaks watch cache loading [merged]

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