feat: add --profile global CLI flag for startup profile selection

[A-Souhei]

Summary

• Adds --profile <name> as a global CLI flag so users can select a profile at startup (e.g. vuhitracode --profile default --agent alice)
• Middleware validates profile name format and existence, setting it before the app bootstraps
• TUI and run commands re-apply the profile to their resolved project directory (fixing mismatch when --dir or a project path argument is used)
• Adds documentation for --profile in cli.mdx and profiles.mdx

How it works

vuhitracode --profile <name>           # set profile for TUI
vuhitracode --profile <name> --agent alice  # set profile + initial agent
vuhitracode --profile <name> run --dir /path "message"  # set profile for run in specific dir

The --agent flag already existed — this PR adds the missing --profile counterpart.

Changes

File	Change
packages/opencode/src/index.ts	Global --profile option + middleware validation
packages/opencode/src/cli/cmd/run.ts	Re-apply profile after --dir resolution
packages/opencode/src/cli/cmd/tui/thread.ts	Re-apply profile after project dir resolution
packages/web/src/content/docs/cli.mdx	Document --profile flag with examples
packages/web/src/content/docs/profiles.mdx	Add CLI section for --profile