docs: merge documentation improvements from dev to main (#81)

* docs: improve documentation structure with unified command chains and cross-linking (#79)

Co-authored-by: Dominikus Nold <djm81@users.noreply.github.com>

* docs: add integrations overview guide (optional task 6.4)

- Create integrations-overview.md with comprehensive overview of all integrations
- Add links from integration guides to integrations-overview.md
- Add link to integrations-overview.md in docs/README.md
- Complete optional task 6.4 from improve-documentation-structure change

* docs: fix linting errors in integrations-overview.md

- Fix MD036 warnings by converting emphasis to proper headings
- Fix MD040 warning by adding language specifier to code block

* docs: simplify README and add links to new documentation

- Update website links to specfact.com / .io / .dev
- Add GitHub Pages docs link: https://nold-ai.github.io/specfact-cli/
- Remove version info section (avoids outdated info)
- Simplify content - remove verbose sections, add links to docs instead
- Add links to new documentation:
  - Command Chains Reference
  - Common Tasks Quick Reference
  - AI IDE Workflow Guide
  - Integrations Overview
- Improve onboarding with clear path for new users

* docs: add prominent SpecFact domain links with context

- Add specfact.com, specfact.io, specfact.dev links prominently at top
- Add domain purpose context (commercial, ecosystem, developer community)
- Highlight specfact.dev for developers
- Add GitHub Pages docs link
- Improve user navigation to appropriate resources

* docs: update Quick Start with correct IDE setup workflow

- Add Step 2: Initialize IDE integration (specfact init --ide)
- Update Step 3: Use slash commands in IDE or CLI
- Add realistic timing expectations (10-15 min for typical repos)
- Explain what init does (copies prompts, makes slash commands available)
- Add link to AI IDE Workflow Guide
- Remove unrealistic '60 seconds' claim

* fix: correct heading level for SpecFact Domains section

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Co-authored-by: Dominikus Nold <djm81@users.noreply.github.com>

Author: djm81