- Add ShareMergeMode::RejectAll variant to reject all incoming shares
- Trim server suffix from share IDs when updating local sheet info
- Sign vault as modified after successful share mapping merge
- Fix get_current_sheet_name call to use correct parameter value

Update file extensions for sheet, share, member, and virtual file
metadata to use new custom extensions (.st, .sre, .json, .vf) instead of
.bcfg. Also update client-side file extensions for latest info and local
sheets.

Use SERVER_SUFFIX_MEMBER_INFO_NO_DOT constant instead of literal "toml"
string for member info file extension check

- Rename `vault_admin_list` to `vault_host_list` in config and actions
- Add `#[serde(rename)]` attributes to all data structures for shorter
  JSON keys
- Update field renames in LocalConfig, LatestFileData, LatestInfo,
  LocalSheetData, Member, SheetData, Share, and VirtualFileMeta

The share ID generation no longer includes the sheet file suffix. This
simplifies share names to just "sharer@random" format.

- Add `rand` dependency for generating share IDs
- Update share path to include sheet name subdirectory
- Add mutable accessor for sheet ID mapping
- Add sheet_share module to vault data structures

- Delete InputPackage struct and related types
- Remove inputs field from SheetData
- Remove input management methods (add_input, deny_input, accept_import)
- Remove export functionality (output_mappings,
  find_longest_common_prefix)
- Update tests to remove input-related assertions
- Clean up unused imports and dependencies

Make server config fields optional and provide default values when
missing. This ensures backward compatibility and graceful handling of
partial configuration.