feat(sync): add include and metadata-based sync rules

[veryCrunchy]

User problem

Sync pairs expose ignored patterns, but users also need positive inclusion rules and filtering based on file metadata. Examples include syncing only documents, excluding videos above a chosen size, or including only selected extensions.

Acceptance criteria

• Support explicit include and exclude rules without ambiguous implicit behavior.
• Match paths or glob-like patterns, hidden-file and hidden-folder state, extension, authoritative MIME or media type, minimum and maximum file size, and file versus directory.
• Define deterministic precedence when include and exclude rules overlap.
• Make the behavior of unmatched files explicit for every rule mode.
• Preview which files will sync, which will not, and which rule made each decision.
• Use consistent, documented case-sensitivity behavior across supported platforms.
• Never interpret a newly out-of-scope file as a deletion to propagate to the other side.
• Re-evaluate safely when metadata changes, including size growth and extension-changing renames.
• Persist rules in a versioned, migration-safe sync configuration.
• Existing sync pairs can adopt rules without deletion and recreation.
• Add bounded tests for overlapping rules, hidden paths, unknown MIME types, missing sizes, renames, and configuration migration.

Relationships

• Parent: [EPIC] Files client and advanced sync #11
• Complements hidden-file and exclusion work in [SYNC-003] Hidden files and exclusion rules #109.
• Coordinates with editable sync-pair settings in [SYNC-004] Update existing sync-pair settings #110.