chore: rebrand application from LevelUp to ClimbStack (#153)

[GiZano]

Rebrands the application from LevelUp to ClimbStack across configuration, UI, documentation, and metadata, while preserving the Android package name as com.gizano.levelup and ensuring backward compatibility for local storage keys.

Fixes #153

Summary of Changes

• App config & package: Updated app name and slug in app.json, package.json, and package-lock.json. Kept Android package name as com.gizano.levelup.
• UI & Links: Updated app header, About dialog, Star on GitHub (https://github.com/ClimbStack/climbstack-app), and Submit Issue links in SettingsScreen.tsx.
• Storage: Added @climbstack/* keys with automatic fallback to @levelup/* to prevent data loss.
• Calendar: Updated calendar title format with backward fallback.
• Documentation & Workflows: Updated README.md, CONTRIBUTING.md, ROADMAP.md, SECURITY.md, AUTHORS, CITATION.cff, issue templates, CI workflow, and tutorial typst/pdf.

AI Generation Disclosure

This pull request and description were generated by an AI agent.

• Tool / Agent: Antigravity CLI
• Model: Gemini 3.1 Pro
• Scope: All modifications in this PR were AI-generated based on issue [FEAT] Rebranding: rename LevelUp to ClimbStack #153 specifications.

[codecov]

Codecov Report

❌ Patch coverage is 75.67568% with 9 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/screens/SettingsScreen.tsx	0.00%	9 Missing ⚠️

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