fix(cli): resolve common UX papercuts in the CLI

[usehoplite]

Summary

Audited the main CLI user flows (init, ingest, synthesize, export, validate, status, jobs, config) for common UX papercuts and fixed the highest-impact, verifiable ones. All fixes are small and CLI-scoped.

What changed

• distill-align init now works without the run subcommand. The README and CLI reference document distill-align init (with --path/--name), but the bare command previously exited with code 2 and printed nothing. init run is preserved for compatibility.
• The documented global --config flag is now honored. It was silently ignored (config was always auto-discovered); a missing explicit file now errors cleanly.
• Invalid --mode (synthesize) and --status (jobs list) values now produce a helpful message listing valid choices instead of a raw ValueError traceback.
• export --format preference no longer crashes. The README quick start documents this command, but preference was missing from the ExportConfig format literal, so it died with a Pydantic ValidationError. Unknown formats now get a clean error listing supported formats.
• Non-array JSON inputs to synthesize/export/validate are rejected with a clear message instead of a TypeError; empty inputs emit a warning.
• ingest fails loudly on empty input (empty dir or no supported files) instead of silently writing an empty chunks.json that poisons the downstream pipeline.
• status reports provider keys for all documented providers (Anthropic, Gemini, Azure, generic DISTILL_) instead of only OpenAI — previously it said "Not set" even when ANTHROPIC_API_KEY was configured.
• config show reports unparseable config files gracefully instead of a raw traceback.
• Fixed an invalid tab character in the generated config template that made every distill-align init config unparseable YAML (the init → config show flow was broken end-to-end).

Verification

• 11 new regression tests in tests/unit/test_cli.py covering each fix.
• Full suite: 201 passed, 8 skipped (unit + integration + property).
• ruff check and ruff format --check clean on all changed files; mypy clean on src/distill_align/cli/main.py.
• Manually smoke-tested the previously-broken init → config show flow and the --config flag.