Track Wave 2: Remove deprecated sync StorageProvider methods

[diberry]

What

Remove the 12 deprecated synchronous methods from StorageProvider interface.

Why

Sync methods were kept in Wave 1 for backward compatibility. Wave 2 should remove them to simplify the interface and eliminate sync I/O paths.

Methods to Remove

readSync, writeSync, existsSync, listSync, isDirectorySync, mkdirSync, statSync, appendSync, deleteSync, renameSync, copySync, deleteDirSync

Tracking

• From FIDO's repo health review of PR feat(sdk): StorageProvider abstraction — complete migration + example providers bradygaster/squad#640
• All callers must migrate to async versions first
• Need ESLint rule to prevent new sync usage

[github-actions]

🏗️ Squad Triage — Flight (Lead)

Issue: #113 — Track Wave 2: Remove deprecated sync StorageProvider methods
Assigned to: Flight (Lead)
Reason: No specific domain match — assigned to Lead for further analysis

@copilot evaluation: No strong capability match — routed to squad member.

Team roster:

• Flight (Lead) → label: squad:flight
• Procedures (Prompt Engineer) → label: squad:procedures
• EECOM (Core Dev) → label: squad:eecom
• FIDO (Quality Owner) → label: squad:fido
• PAO (DevRel) → label: squad:pao
• CAPCOM (SDK Expert) → label: squad:capcom
• CONTROL (TypeScript Engineer) → label: squad:control
• Surgeon (Release Manager) → label: squad:surgeon
• Booster (CI/CD Engineer) → label: squad:booster
• GNC (Node.js Runtime) → label: squad:gnc
• Network (Distribution) → label: squad:network
• RETRO (Security) → label: squad:retro
• INCO (CLI UX & Visual Design) → label: squad:inco
• GUIDO (VS Code Extension) → label: squad:guido
• Telemetry (Aspire & Observability) → label: squad:telemetry
• VOX (REPL & Interactive Shell) → label: squad:vox
• DSKY (TUI Engineer) → label: squad:dsky
• Sims (E2E Test Engineer) → label: squad:sims
• Handbook (SDK Usability) → label: squad:handbook
• Ralph (Work Monitor) → label: squad:ralph
• @copilot (Coding Agent) → label: squad:copilot

To reassign, remove the current squad:* label and add the correct one.