tracker: prove compatibility matrix for fork and Automattic consumers

[chubes4]

Goal

Track the compatibility proof needed before treating the Extra-Chill fork as the polished update path for the Automattic repository and downstream consumers.

Required surfaces

• bbPress topic creation.
• bbPress reply creation.
• bbPress topic/reply editing.
• bbPress media upload and paste behavior.
• bbPress autosave/draft restore/reply switching.
• Pattern insertion and initial pattern seeding.
• Synced pattern reference insertion/rendering boundary.
• Fullscreen chrome, Escape-to-exit, and scroll lock.
• Existing comments/BuddyPress behavior that should not regress.
• Automattic PR branch behavior against the current Automattic repo baseline.

Acceptance criteria

• A concise test matrix exists with pass/fail evidence.
• Known gaps are filed as issues instead of hidden in PR notes.
• The matrix distinguishes fork-only shipped behavior from Automattic-upstream-ready behavior.
• Any private/downstream proof stays out of public terminology while still validating the generic adapter contract.