feat(cli): add dispatch path to print a session directory

[jongio]

What

Adds a dispatch path command that prints only a session's working directory, so you can change into it from a subshell:

cd "$(dispatch path 0a1b2c3d)"   # by ID or short prefix
cd "$(dispatch path my-alias)"   # by alias
cd "$(dispatch path --last)"     # most recently active session
cd "$(dispatch path --current)"  # match the current repo and branch

Why

dispatch info prints a full summary and dispatch open --print prints a resume command. Neither gives you just the directory, so scripting a cd into a session folder meant parsing output. path fills that gap with a single-line, cd-friendly result.

Details

• Resolves the session the same way open does (full ID, alias, short ID prefix, --last, --current) by reusing open's resolver seams, so matching rules stay identical.
• Writes the absolute directory plus a trailing newline and nothing else.
• Exits with an error if the session has no recorded directory or if that directory no longer exists on disk, so cd "$(...)" fails loudly instead of landing somewhere wrong.
• Wires the command into the CLI dispatch switch, the four shell completion lists (bash, zsh, fish, powershell), the usage banner, the man examples, the README, and the changelog.

Tests

• parsePathArgs table tests: id, alias, --last, -l, --current, and the error cases (no selector, combined selectors, extra args, unknown flag).
• runPath tests via the seam stubs: resolve by ID, by alias, --last, --current, empty-directory error, missing-directory error, unknown ID.

Verification

go build ./..., go vet ./..., go test ./..., golangci-lint run, and mage deadcode all pass.

Closes #330