docs: lead with the case a lock cannot cover

[cardmagic]

Framing fix to the first screen and the fit sections. No API documentation was
rewritten, and no runtime code changed.

The lead example

A cart append needs one thing from one value. The ticket sale needs three:

• it must never go below zero;
• it must give the seat back if the buyer does not pay within ten minutes; and
• it must show the current count to everyone watching the page.

The first is one UPDATE statement. The second is an expiresAt column plus a
sweeper. The third is a push on every path that changes the number. The
combination is the argument, and the example now shows all three in one class:
the guard, this.schedule({ at, key }), and broadcastValue(this.remaining).

Answering the objection where it is asked

## Why not just use a transaction and a row lock? now sits in the first
screen. It concedes first, in the first sentence, because a concession is what
buys the right to be believed in the paragraph after it. Then it argues scope
rather than discipline:

A lock is scoped to one transaction, on one connection, in one process. The
ticket sale above leaves that scope on one line: the hold expires in ten
minutes, and no transaction stays open for ten minutes. A setTimeout does
not cover it either, because it dies with the process.

Any column named expiresAt, scheduledAt, or nextRunAt is evidence that
the critical section already outlived the lock that was supposed to cover it.
What follows such a column is a sweeper that looks for due rows, and then a
race between that sweeper and the next writer of the same row.

Arguing "you might forget the lock" would lose that exchange, because the reader
answers "so remember" and they are right.

Also

• ## Is it worth installing here? moves into the first screen, and says who
  should not use this, specifically.
• The existing "Not a replacement for SQL transactions" callout asserted the
  limit without showing where it bites. It now names the cases and links to the
  section that argues them.
• The Comparison table already carried a SQL transaction or row lock row, so
  it is unchanged.
• The realtime section concedes writing and then sending on your own socket
  before explaining the two gaps: two sends can arrive out of order, and a send
  is not part of the write.

Validation

The lead example was executed against this branch as a temporary test, not read
for plausibility: three concurrent reserves serialize to remaining 97, a
repeat reserve for the same buyer returns false, and expire returns the seat
to 98. The scratch test was removed before committing.

pnpm run check clean, pnpm test 343 passed and 13 skipped.

The Ruby counterpart is cardmagic/solid-objects-ruby#54. Verifying its example
turned up a bug in the shipped homepage copy: it stores Time.current in actor
state, which Ruby state serialization rejects, so that reserve never commits.
The JS homepage example stores Date.now() and is unaffected.

[greptile-apps]

Greptile Summary

The PR reframes the README around coordination that outlives a transaction and synchronizes the package version for the documentation release.

• Replaces the introductory cart example with a scheduled, realtime ticket-sale example.
• Moves transaction-scope and adoption guidance into the opening sections.
• Clarifies that realtime publication is recorded atomically but delivered separately with at-least-once semantics.
• Updates the changelog and version metadata to 0.14.3.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
README.md	Reworks the introductory narrative and correctly resolves the prior ambiguity between durable publication recording and subsequent at-least-once delivery.
CHANGELOG.md	Documents the 0.14.3 README rewrite and corrected realtime-delivery language.
package.json	Updates the package version from 0.14.2 to 0.14.3.
src/version.ts	Keeps the exported runtime version synchronized at 0.14.3.

_{Reviews (2): Last reviewed commit: "release: use 0.14.3, not 0.15.0" | Re-trigger Greptile}