Unify session cleanup commands with flags instead of separate subcommands

[jcleira]

Description

If Partio has overlapping cleanup commands (e.g., reset and clean, or similar), consolidate them into a single partio clean command with flags: default behavior cleans sessions at current HEAD, --all for repo-wide orphan cleanup, --session <id> for single-session cleanup, --dry-run for preview, and --force to skip confirmation. Deprecate any redundant command with a Cobra Deprecated field so users see an automatic warning and migration path. Make --all and --session mutually exclusive.

Why

Overlapping cleanup commands with similar-but-different scope confuse users and increase support burden. A single unified command with explicit flags is easier to document, discover, and reason about.

Source

• Origin: Deprecate reset command entireio/cli#720
• Detected from: entireio-cli-pulls

Target Repos

• cli
• docs

Acceptance Criteria

• Single clean command handles current-HEAD, all-orphan, and single-session cleanup via flags
• --all and --session flags are mutually exclusive and produce a clear error if both are passed
• --dry-run outputs what would be deleted without modifying state
• Any deprecated command prints an automatic deprecation warning pointing to the replacement
• Tests cover: nothing to clean, force mode, dry-run, session-specific cleanup, mutual exclusion of flags

Context Hints

• cli/cmd/

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