chore: prepare v0.7.0

[JtheGunner]

Moves the [Unreleased] changelog entries under [0.7.0] and updates the compare links.

Contents

• omnishell tui: the terminal UI (module browser, toggling, options editor, plan preview with hand-off to apply), see OMNIS-14.
• apply says "Nothing to apply" when it finds nothing to do.
• Fixes: package manager output no longer leaks into read-only commands (OMNIS-35: Keep package manager output out of read-only commands #41), omnishell set writes valid TOML escapes (OMNIS-38: Write TOML escapes instead of Go escapes for config values #44), list cleans manifest text.

Test plan

• go vet ./... and go test ./... -race -count=1 pass on this branch.
• After merging, tag v0.7.0 on the merge commit; release.yml verifies the tag is on main and runs GoReleaser (archives, Homebrew formula).