feat: ANSI escape and progress bar stripping

[bug-ops]

Parent

Epic: #426

Summary

Strip ANSI escape sequences and progress bar output from all tool outputs as a baseline preprocessing step before command-specific filters.

Expected Savings

5-15% baseline on all outputs, 85-95% on progress-heavy commands (cargo build with progress, wget, pip install).

Behavior

• Strip all ANSI escape codes: \x1b\[[0-9;]*[a-zA-Z]
• Strip carriage return progress lines: lines ending with \r that rewrite the same terminal line
• Collapse consecutive blank lines to max 2
• Strip common progress patterns: [=====> ] 45%, Downloading..., Compiling N/M

Implementation

• sanitize_output(raw: &str) -> String function in filter.rs, applied before any command-specific filter
• Should be fast (single-pass regex or manual char iteration)
• Already partially handled by terminal — verify what execute_bash captures vs raw PTY

Acceptance Criteria

• ANSI codes stripped
• Progress lines collapsed
• Blank line normalization
• Performance: < 1ms for 100KB output
• Unit tests