[AAASM-4187] 📝 (readme): Reword intro from router model to aggregation model

[Chisanan232]

Description

Rewords the README.md intro paragraph from the superseded router/link model
to the current aggregation model, resolving a doc self-contradiction that was
a residual of AAASM-4174.

AAASM-4174 rewrote the README's "How content reaches the site" section (and
AGGREGATION.md) to describe the aggregation pipeline — the hub builds each
component's docs with its native toolchain and mounts them under stable subpaths
(/core/, /python-sdk/, /node-sdk/, /go-sdk/) with a unified Pagefind index,
deploying one combined site. The intro paragraph was left describing the old model
("the hub is the central router … linking to each component's own docs site root
rather than duplicating their content"), so it contradicted the same README's
pipeline section and AGGREGATION.md.

What changed: the intro now reads that the hub "aggregates the docs of every
independently versioned component — building each with its own native toolchain and
mounting it under a stable subpath (/core/, /python-sdk/, /node-sdk/, /go-sdk/)
— into one unified, searchable site," mirroring the pipeline section and
AGGREGATION.md. One line changed in substance; no other content touched.

.claude/CLAUDE.md — deferred as a follow-up. That file also carries the
router/link framing, but it is threaded through multiple sections (the "What this
repo is" description, the versioning-channel-model note, and the whole
"Documentation conventions" philosophy, which is built around "link out, don't
duplicate"). That is a substantive multi-part rewrite, not a quick analogous
same-fix reword, so it is intentionally left out of this PR to keep scope tight.

Also noted (out of scope, potential further follow-up): a few other README
sections outside the intro still use router/link phrasing — the "What's inside"
Documentation-index bullet, the component-map "router page" paragraph, and the
"content sourced from" bullet. These describe the documentation.md index page's
routing role and were left untouched, as this ticket is scoped to the intro
paragraph only.

Type of Change

• 🐛 Bug fix (correcting inaccurate or missing content)

Related Issues

• Related Jira ticket: AAASM-4187

Documentation Checklist

• cd docs && mdbook build passes locally with no warnings
• All internal cross-links verified
• Page registered in docs/src/SUMMARY.md (N/A — README, not an mdBook page)
• Self-hosted instructions not included (SaaS-only scope)
• "Last reviewed" footer updated with today's date (N/A — README has no footer)
• Commits follow GitEmoji convention and are small / atomic

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Chisanan232]

Claude Code review — AAASM-4187

Verdict: approve-ready (comment-only; Pioneer sign-off yours).

• CI: No red. MERGEABLE. mdbook build clean (only the pre-existing mdbook-mermaid version-skew notice).
• Scope: Matches ticket. README intro reworded from the superseded router/link model ("central router … linking to each component's site root rather than duplicating") to the aggregation model ("aggregates the docs of every independently versioned component … under a stable subpath /core/ /python-sdk/ /node-sdk/ /go-sdk/ … into one unified searchable site"), mirroring AGGREGATION.md + the pipeline section AAASM-4174 wrote. No more "router"/"site root"/"rather than duplicating" in the intro.
• Side-effects: None — README.md intro only (+4/−3, 1 substantive line).
• Correctly scoped out (flagged as follow-ups, not over-reached): .claude/CLAUDE.md router framing (threaded through multiple sections — substantive rewrite); other README sections describing the genuine documentation.md index-page routing role.

— Claude Code review