Add Technological Foundations documentation page

[evnchn]

Motivation

The homepage Features section currently links out to external websites for core technologies (vuejs.org, quasar.dev, fastapi.tiangolo.com, tailwindcss.com). This is an SEO problem: outbound links on high-traffic pages bleed PageRank to third-party domains instead of keeping visitors within the NiceGUI documentation. Search engines also favor sites with strong internal linking over those that immediately send users elsewhere.

Additionally, NiceGUI's technology stack explanations are currently scattered across markdown files that most users never see:

• README.md lines 95–106, 143–154 — "Why?" section and "Architecture" section
• CONTRIBUTING.md lines 21–28 — "Tech Stack" bullet list
• DEPENDENCIES.md — version list of web dependencies

None of this information is on the documentation website itself. This PR creates a proper, user-facing documentation page that explains the technology choices and how they fit together.

Implementation

New section_foundations.py documentation page — "Technological Foundations" with six sections, each using @doc.part() with side-by-side grid layout (2fr text / 1fr visual):

Section	Text content	Visual
UI Framework	Vue.js role, JustPy inspiration, custom Vue components, alpha-level other-framework support	Mermaid diagram: NiceGUI Element → Vue Component → Browser DOM
Component Library	Quasar's 70+ components, __init__ params vs .props(), occasional renames	NiceGUI-to-Quasar element mapping table with .props() examples
Backend	FastAPI/Starlette/Uvicorn stack, REST mixing, ui.run_with(), ASGI mounting	Mermaid diagram: NiceGUI + Other Routes → FastAPI → Uvicorn ← Other ASGI Apps
Real-Time Communication	Socket.IO transports, fallback, reconnection, rooms; Outbox batching, message IDs, rewind/replay, ack pruning	Mermaid diagram: NiceGUI → Outbox → Socket.IO → Browser with feedback loops
Styling	Tailwind CSS (CDN, most features), UnoCSS (lighter, mini preset), Quasar CSS (built-in, lightest)	Progress bar comparison: Features vs Lightweight for each engine
How It All Fits Together	Summary tying all pieces together	—

Homepage link updates:

• Features section links (Vue, Quasar, FastAPI, Tailwind CSS) now point to the corresponding foundations sections instead of external websites
• "Python 3.10+" replaced with "real-time sync via Socket.IO" (links to foundations)

Documentation overview: added import and tile for the new section.

Progress

• I chose a meaningful title that completes the sentence: "If applied, this PR will..."
• The implementation is complete.
• If this PR addresses a security issue, it has been coordinated via the security advisory process.
• Pytests have been added (or are not necessary).
• Documentation has been added (or is not necessary).

Note: This PR depends on #5813 (SEO support) being merged first, as both PRs modify website/main_page.py and the SEO improvements provide the foundation for the discoverability goals here.

[evnchn]