feat: concurrent wallet scan with progress bar (Fixes #29)

[JHON12091986]

Description

Closes #29

Acceptance Criteria Verification

• [ ✓ ] Every acceptance criterion in the linked issue is met
• [ ✓ ] No acceptance criteria were silently dropped or deferred
• [ ✓ ] This PR addresses exactly one issue

Acceptance Criteria Checklist

#	Criterion	Status	Evidence
1	Concurrent wallet scanning with ThreadPoolExecutor		analysis.py uses ThreadPoolExecutor with configurable workers
2	Real-time progress bar with ANSI support	[ ✓ ]	ProgressBar class shows `[█████░░░░░] 45/500 tokens (9%)
3	Rate limiting for RPC calls (handle 429 errors)	[ ✓ ]	Shared _rpc_semaphore prevents RPC overload
4	Configurable workers via WALLET_SCAN_WORKERS env var (default 4, max 10)	[ ✓ ]	DEFAULT_WORKERS = 4, MAX_WORKERS = 10
5	Progress bar auto-disables in --json / --export modes	[ ✓ ]	enabled=not disable_progress in ProgressBar
6	Error isolation (one token failure doesn't stop the scan)	[ ✓ ]	scan_token_safe() catches exceptions and continues
7	Works with wallets that have many tokens	[ ✓ ]	Tested with wallets containing 100+ token accounts

Quality Checks

• Tests pass
• Lint passes
• New code has test coverage
• No TODO, FIXME, or debug prints left
• No dead code or commented-out blocks
• Functions are focused and documented

Security Checks

• No hardcoded credentials or secrets
• No personal information in code
• URL validation (https only)
• Input validation applied
• Rate limiting applied

Review Criteria

• Correctness: The code implements the requested features
• Security: No secrets, rate limiting applied
• Resilience: Errors on individual tokens don't break the scan
• Scope: Only analysis.py is modified