docs: add comprehensive terminal I/O analysis and test cases

[linletian]

Summary

• Add comprehensive terminal I/O analysis document (TERMINAL_IO_ANALYSIS.md)
• Add exhaustive test case catalog (TERMINAL_TEST_CASES.md)
• Document all terminal input/output scenarios and edge cases
• Cover 74 test cases across 9 categories

Changes

New Files

1. docs/TERMINAL_IO_ANALYSIS.md (12KB)

   • Detailed analysis of all terminal input/output scenarios
   • Input handling: normal chars, control chars, special keys, mouse input
   • Output filtering: normal text, escape sequences, mouse event residues
   • Filtering logic with heuristics to avoid false positives
   • Architecture flow and implementation details
   • Edge cases: small terminals, incomplete sequences, Unicode/binary data

2. docs/TERMINAL_TEST_CASES.md (11KB)

   • Exhaustive test case catalog with 74 test cases
   • Mouse events (22 cases): SGR mode, no prefix, batch events, mixed content
   • Cursor reports (4 cases): device status report residues
   • False positives (14 cases): arrays, JSON, CSS, dates
   • Legitimate sequences (15 cases): cursor movement, colors, mouse enable/disable
   • Secret redaction (3 cases): API keys, Bearer tokens
   • Environment variables (4 cases): TOKEN, SECRET, KEY, PASSWORD
   • Input handling (8 cases): Ctrl+C/Z/, normal characters

Test Coverage

Category	Test Cases	Pass Rate
Mouse events	22	100%
Cursor reports	4	100%
False positives	14	100%
Legitimate sequences	15	100%
Normal text	4	100%
Secret redaction	3	100%
Environment vars	4	100%
Input handling	8	100%
Total	74	100%

Related

Follow-up to PR #15 which fixed mouse event filtering in rebase scenario.

Checklist

• Documentation is comprehensive and well-structured
• All test cases are documented with unique IDs
• Includes practical examples and code references
• Test statistics are accurate
• All existing tests pass