chore: update docs for system-wide installation and expand test coverage

Summary

This MR updates project documentation to reflect modern installation workflows (global uv tool install) and significantly expands test coverage across the CLI codebase.

Changes

Documentation

• README.md & docs/user-manual.md
  • Added system-wide installation instructions via uv tool install and pipx
  • Added development installation section with uv sync
  • Updated all command examples from uv run corpus-client … to corpus-client …
  • Added new corpus-client status command to the reference list
  • Added step-by-step record upload guide
  • Expanded FAQ with common questions (multiple directories, file size limits, non-interactive credentials)

Bug Fix

• src/corpus_client_cli/job.py
  • Fixed Python 2-style exception tuple syntax (except A, B: → except (A, B):)

Code Quality

• src/corpus_client_cli/upload.py
  • Minor line-length formatting fix

Test Coverage

• tests/test_extracted_text_upload.py

  • ExtractedTextState edge cases (load errors, legacy log, save failures)
  • parse_dots_ocr edge cases (footer, image caption/footnote strings, empty text, reading order)
  • GeneralizedExtractedTextUploader tests (409 response, non-200 errors, generic exceptions)

• tests/test_output.py (new file)

  • Tests for output() JSON and non-JSON modes
  • Tests for log() stderr output

• tests/test_retry_logic.py

  • with_retry edge cases (non-tuple results, exhausted retries, zero max retries)
  • format_error_payload comprehensive tests (strings, lists, dicts, validation errors)
  • _format_validation_item tests
  • read_response_payload and read_error_message async tests

• tests/test_s3_upload.py

  • upload_single_shot tests (non-list category IDs, error responses, exceptions)
  • process_file tests (chunk failure, finalize failure, exception with cleanup)
  • UploadState tests (job path restore, progress log exception handling)
  • finalize_upload response payload error handling

• tests/test_upload.py

  • resolve_file_pattern tests (no pattern, extensions, recursive glob)
  • ProgressTracker tests
  • process_file tests (not found, validation fails, finalize fails, success path)

• tests/test_upload_state.py

  • Load with progress log, save throttling, force save, corrupted log handling, append log errors

• tests/test_validation_fail_fast.py

  • Extensive validation helper tests (_normalize_mime_type, _words, _looks_like_repeated_characters, _size_limits_for_media_type, _guess_mime_type)
  • validate_title, validate_description, validate_source_fields, validate_release_rights, validate_coordinates, validate_inline_text_content tests
  • validate_file_before_upload edge cases (OSError, size limits, MIME detection, duration checks)