docs: restructure README for clarity and professionalism

[theaayushstha1]

Summary

Standalone README restructure ahead of the hackathon submission — pure documentation change, no code touched.

• Single, consistent heading hierarchy with a clickable TOC at the top — judges can jump to whichever section matters.
• Killed every duplicate section — Quickstart appeared twice, Modes vs Mode taxonomy appeared twice, Grounding gate appeared twice, UI vs UI status, Implementation notes vs Architecture. Each topic now lives in exactly one place.
• Consolidated Modes + trust tags + tiers into one section near the bottom (pitch first, taxonomy second).
• Merged Memory + Managed-Agents-memory + Memory CLI into one clean section with a single table for the lifecycle commands.
• Collapsed the giant capability matrix inside <details> so the shipped/partial/roadmap legend stays visible but the wall of rows doesn't drown the page.
• Promoted Demo + 60-second quickstart to the top so judges hit it before the trust-tag taxonomy.
• Trimmed the Docs list to judge-relevant items only — dropped TESTIMONIAL, FLAG_PLANT, REHEARSAL, RISKS, ONBOARDING, SUBMISSION, the redundant Token discipline section, and the hackathon-internal "Open backlog" PR-number noise.

What did NOT change

• Every concrete claim, file pointer, code block, mermaid diagram, and benchmark number is preserved.
• Reference run numbers ($0.46 total spend, 2 of 3 non-skeleton matches, file path) unchanged.
• Hero-case narrative, grounding-gate thresholds, frozen 7-class taxonomy, memory stack details unchanged.

Test plan

• Render the README on github.com/LucasErcolano/BlackBox/tree/docs/readme-restructure and skim
• Click each TOC anchor — confirms heading IDs all resolve
• Expand the capability <details> block — confirms the full table is intact
• Confirm every internal link (docs/SMOKE_TEST.md, SCOPE_FREEZE.md, etc.) still resolves

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