perf: reduce Process URI estimation overhead

[tom-sapletta-com]

Ticket: ticket-008

Summary

• sample commands and PID trees at 1 Hz by default
• extend the append-only event chain from a bounded tail read
• add regression coverage for defaults and read amplification

Validation

• PYTHONPATH=src python -m pytest (10 passed)
• PYTHONPATH=src ./project/governance-check.sh (GOV-PASS)

[tom-sapletta-com]

Superseded by #3. The four implementation/test blobs were verified byte-for-byte identical; #3 rebuilds only the delivery history so the plan commit precedes implementation. Local tests: 10 passed; governance: 0 errors/warnings.