Docs: README front door buries quickstart, lacks a TOC, oversells the '90-Second Proof'

[codeforester]

Goal

Restructure README.md so a first-time visitor reaches a working quickstart
before philosophy/scope content, can navigate the ~1968-line file, and isn't
given an overstated speed claim for the fastest onboarding path.

Background

A documentation review focused specifically on new-user first impressions
found:

• README.md has no table of contents despite 18 top-level ## sections and
  ~1968 lines — the single biggest scannability failure for a doc this long.
• README.md:21-61 — between the one-paragraph pitch (lines 8-19) and the
  "Start Here" quickstart (line 62), the README inserts "Why Base Exists"
  (philosophy/links) and "Source Control And Forge Support" (Mercurial/
  Perforce-out-of-scope, GitHub-primary caveats) content. A first-time reader
  hits governance/scope material before seeing a single runnable command.
• README.md:64-117 — the "90-Second Proof" section's own instructions
  (read manifest-review guidance, run trust status, hand-copy a printed
  digest into trust allow, repeat the clone/review/trust-allow cycle for a
  second repo) realistically take several minutes of careful reading, not 90
  seconds — an overstated claim right at the top of the front door.
• README.md:329-1291 — "Product Layers And Shipped Commands" is one
  continuous ~960-line section (nearly half the file) that inlines the full
  command reference, duplicating docs/command-reference.md and
  docs/technical-overview.md, and forces anyone scrolling past the pitch to
  wade through ~1,000 lines before reaching Compatibility, Shell Startup, or
  License.
• README.md:8-11 — the opening value proposition leads with the undefined
  term "local operating contract" in a dense multi-verb clause instead of a
  one-sentence plain-English gloss a newcomer can parse in one pass.

Scope

• README.md structure and ordering only (no content-accuracy changes
  required here; see companion issues for factual fixes).

Acceptance Criteria

• README.md has a table of contents (or equivalent jump-nav) near the
  top.
• The pitch is immediately followed by a runnable quickstart, with
  philosophy/scope caveats moved after it (or linked out rather than
  inlined).
• The "90-Second Proof" section's time claim matches its actual steps, or
  the steps are trimmed to genuinely fit the claim.
• The ~960-line "Product Layers And Shipped Commands" section is either
  trimmed to a summary with a link to docs/command-reference.md /
  docs/technical-overview.md, or clearly marked as a skippable deep
  reference so it doesn't block a first read-through.
• The opening pitch defines "local operating contract" (or an equivalent
  term) in plain language on first use.

Validation

git diff --check; read the rendered README top-to-bottom and confirm a
first-time reader reaches a runnable command within the first ~50 lines.

Non-Goals

• Rewriting the full command reference content itself.
• Changing the underlying product positioning or terminology choices beyond
  defining them on first use.

Project Metadata

• Priority: P1
• Size: M
• Area: Docs
• Initiative: Adoption Polish
• Agent Assignment: Human first (structural/editorial judgment call)