docs: neutralise local paths and relabel spelling convention

[tanem]

Summary

• Replace ~/Code/mt5-pnl-cli and ~/Code/mt5-pnl-exporter personal path references with generic <repo-root> / <mt5-pnl-exporter-root> tokens across plan and spec docs.
• Replace the ~/Dropbox/mt5/… example snapshot path with a generic ~/snapshots/mt5.json.gz.age (consistent with the exporter's own example).
• Relabel NZ English → British/Commonwealth English throughout CLAUDE.md, CONTRIBUTING.md, and historical plan/spec docs (no functional change; clearer label for global contributors).
• Neutralise a NZ timezone example in the README (like NZ → e.g., UTC+12).

No code, logic, or config changes — Markdown docs only. All tests pass.

Scope

All committed docs including historical plan/spec docs, per the project's public audience rule: committed artifacts should not contain the author's personal file paths, OS layout, or personal setup specifics.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.29%. Comparing base (5aa53d5) to head (c852538).
⚠️ Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #6      +/-   ##
==========================================
+ Coverage   78.65%   84.29%   +5.63%     
==========================================
  Files          11       12       +1     
  Lines         431      452      +21     
==========================================
+ Hits          339      381      +42     
+ Misses         75       64      -11     
+ Partials       17        7      -10     

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