fix: restrict Cursor globs to active Flutter AI rules profile

[Wreos]

Motivation

• The previous change added globs front matter to every synced profile, which caused all generated rules/official/*.mdc files to auto-attach to Dart files and could lead to multiple profiles applying simultaneously instead of honoring the single active profile contract.
• The repository’s documented contract requires only rules/flutter-official-ai-rules.mdc to be the auto-attached active profile, so globs must be restricted to that file.

Description

• Removed emission of the globs YAML line from download_rule() in scripts/sync_official_flutter_ai_rules.sh so files written to rules/official/ only contain neutral metadata (description, alwaysApply).
• Replaced the direct cp used to populate the active profile with an awk transform that inserts the globs front matter only into rules/flutter-official-ai-rules.mdc when selecting the active profile.
• Updated checked-in synced artifacts under rules/official/ (flutter-ai-rules-10k.mdc, flutter-ai-rules-4k.mdc, flutter-ai-rules-1k.mdc) to remove the globs front matter so only the active profile auto-attaches.

Testing

• Ran bash -n scripts/sync_official_flutter_ai_rules.sh for a syntax check, which succeeded.
• Verified front matter via automated inspection commands (sed/awk/for f ... sed -n) and confirmed rules/official/*.mdc no longer include globs while rules/flutter-official-ai-rules.mdc contains the expected globs entry.
• Ran an awk cleanup to remove any pre-existing globs lines from rules/official/* which executed successfully in this environment.
• Attempting to exercise live upstream fetches failed in this environment due to remote HTTP 403 responses, so end-to-end network download could not be validated here.

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Codex Task