parity(#261): CLI --format text and a TTY-only indexing progress bar #119

Summary

Upstream semble #261 (b5cdcf0) made two CLI UX additions:

1. --format {json,text} on search and find-related. Text mode prints path:start-end followed by the snippet, or the error string.
2. An indexing progress bar on stderr, shown only when stderr is a TTY (tqdm(..., file=sys.stderr, leave=False)).

csp status

• The CLI is JSON-only. search_output / find_related_output in bin/csp/main.rs always return JSON.
• There is no progress UI. create.rs has no hook in the file loop and the crate has no indicatif dependency.

Proposal

• --format text|json (default json). Text mode handles the {"error": ...} shape and omits the snippet when content is absent (--max-snippet-lines 0).
• A show_progress option threaded through LoadOrBuildOptions / from_path_with_previous, enabled only when stderr is a TTY and never under csp mcp, because MCP owns stdout and the progress bar must not corrupt the protocol stream.

Acceptance

• csp search q --format text prints path:start-end blocks; JSON output is unchanged.
• Piped stderr shows no progress output.