Release 3.1.0: snippet catalogue

[yankikucuk]

Summary

• 78 new snippets (97 in total), adapted to Pine Script v6 from the jeyllani/pinescript and kaigouthro/Pine-Script-VS-Code extensions plus common community patterns: script headers and full declarations, documentation blocks, every input function, plots and drawings, alerts, requests and sessions, strategy risk blocks, indicator sections and collections.
• Every snippet was resolved to plain code and compiled with the TradingView compiler; all of them compile without errors.
• New vitest suite checks unique prefixes, well-formed placeholders and v6 pragmas.
• README rewritten around the feature set with a quick start and the snippet catalogue.
• Version 3.1.0, changelog entry added.

Test plan

• npm test
• npm run build and vsce package
• All 97 snippets compile with the v6 compiler