feat: add z.ai token usage status bar extension

[j4rviscmd]

Summary

• Add VSCode extension that displays z.ai token usage percentage in the status bar
• Implement API key management via VSCode Secrets API (set/clear commands)
• Add caching layer with configurable refresh interval to reduce API calls
• Support custom icon or text label via zaiUsage.useIcon setting
• Automatically invalidate cache when reset time has passed

Changes

src/extension.ts

• Status bar item showing token usage percentage with time-until-reset
• fetchFromApi: fetches /api/monitor/usage/quota/limit with Bearer auth
• fetchUsage: cache-first fetch with fallback to stale cache on API failure
• isCacheValid: invalidates cache when refresh interval elapsed or nextResetTime passed
• Commands: zaiUsage.setApiKey (with verification), zaiUsage.clearApiKey
• Configuration change listener for live refresh interval / icon toggle

Config files

• package.json: extension manifest, commands, configuration schema, CI scripts
• tsconfig.json: TypeScript compiler settings (ES2020, strict)
• biome.json: Biome linter/formatter configuration

Code quality

• Redundant intermediate variables removed (refreshIntervalMs, nowMs, cacheData)
• Section divider comments removed (function names are self-explanatory)
• Inline comments scoped to non-obvious logic only
• Array.isArray guard simplified (covers null/undefined implicitly)
• setCache uses satisfies CacheData for type safety without intermediate variable

Refactoring

• Extract API_URL constant at module level to eliminate magic strings
• Reorder function definitions by dependency for top-to-bottom readability
• Extract applyNoApiKeyState() helper to consolidate duplicated 3-line block (DRY)
• Inline headers in fetchFromApi to reduce nesting
• Align return object literals in fetchUsage for visual consistency
• Annotate return type : void consistently on activate, startInterval, updateStatusBar, and deactivate

Documentation

• Add JSDoc comments (English) to all interfaces: ZaiLimit, ZaiApiResponse, CacheData, UsageData
• Document all interface properties with @ field descriptions
• Add JSDoc to module-level constants: CACHE_VERSION, CACHE_KEY, API_KEY_SECRET, API_URL
• Add JSDoc to setApiKeyCmd and clearApiKeyCmd command callbacks
• Add JSDoc to the onDidChangeConfiguration handler
• All comments and documentation are in English