Add bulk placeholder tool pages, sitemap, tools metadata, and tool workbench

[SH20RAJ]

Motivation

• Provide fast-indexing, low-KD landing pages and lightweight placeholders for many long-tail tool queries to accelerate SEO and launches.
• Centralize placeholder UI and small client-side conversions so new tool routes can be deployed quickly without full feature implementations.

Description

• Added a large set of new route pages (many src/app/.../page.tsx) that render a shared ToolPlaceholderPage for image, text, developer, SEO, YouTube, utilities, and other tool categories.
• Introduced ToolPlaceholderPage and a client-side ToolWorkbench component to display metadata, keyword chips, input/output editors and lightweight conversion logic for many basic tools.
• Updated src/constants/tools.json with a major expansion of tools and categories (version bump, lastUpdated, and totalTools increase) and added a static public/sitemap.xml containing the new routes.
• Small housekeeping: changed lint scripts in package.json to eslint ., removed an unused import in markdown-to-text/page.js, and added docs/seo-low-hanging-fruit-strategy.md describing the launch strategy.

Testing

• Ran eslint via npm run lint against the modified files and addressed reported issues; lint completed successfully.
• Executed a production build with next build to validate route compilation and the app's server/static output, and the build completed without errors.

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Codex Task