emrg: add missing error=True flags in tool error returns and add edit_tool tests

[argszero]

Summary

Fix 5 instances across 4 tools where error returns lacked error=True, and add 8 new tests for the previously-untested edit_tool.

Changes

Bug Fix: Missing error=True in error returns

Tool	Location	Fix
read_tool.py	line 82	Error: no file_path provided -> + error=True
edit_tool.py	line 69	Error: no file_path provided -> + error=True
edit_tool.py	line 71	Error: old_string is empty -> + error=True
write_tool.py	line 49	Error: no file_path provided -> + error=True
bash_tool.py	line 58	Error: no command provided -> + error=True

Previously these returned error=False (the default), making error-checking code unable to distinguish user-facing errors from successful responses. All other error paths in these tools already correctly set error=True.

New Tests: test_edit_tool.py

8 tests covering all major code paths:

• Basic replacement
• replace_all=true
• old_string not found
• Multiple occurrences without replace_all
• Non-existent file
• Directory target
• Empty old_string
• Missing file_path

Verification

• uv run pytest tests/ -v -> 58 passed (8 new, 50 existing)
• uv run python -c "from emrg.client.app import run_client" -> OK
• uv run python -m emrg --help -> OK

[argszero]

✅ LGTM — cycle #9

[argszero]

✅ LGTM — cycle #10

[argszero]

✅ LGTM — cycle #11