fix(tui): use lowercase notes shortcut

[HonestMajority]

Summary

• use lowercase o for project notes in TaskList/project detail
• move linked PR opening to lowercase p in TaskList/project detail and Preview
• update affected status-bar hints and add regression coverage for the linked-PR conflict

Validation

• cargo fmt --check
• git diff --check
• cargo test

Review

• Researcher notes-shortcut-lowercase approved commit 540648d with no findings.