Fold the cursor range guard into the 0.2.0 changelog section

[ryckakas]

Problem

PR #10's fix is on main under ## [Unreleased], which sits above ## [0.2.0]. Tagging
v0.2.0 at current main would put that code inside the release while the changelog calls it
unreleased — inaccurate from the moment the tag exists.

The framing was also wrong independently of the tag. Filing the overflow guard under ### Fixed
tells a reader that some released version was broken. None was: v0.1.0 has no
CursorWalk\Offset namespace, so no published build could reach the arithmetic. The bug was
introduced and closed entirely within the unreleased 0.2.0 work.

Change

• Strip [Unreleased] back to ### Planned — nothing else is pending.
• Fold the substance into 0.2.0's own PositionalFetcher bullet, stated as behaviour rather than
  as a repair: positional cursors are client-supplied, so a non-integer or an out-of-range one
  raises MalformedPageException before the upstream is called.
• Drop the docblock-only ### Changed entry. It described a wording fix to a docblock that is
  itself new in 0.2.0, with no behaviour change — noise for anyone reading the release.
• Correct the same overclaim in 0.2.0's existing hasPreviousPage entry: it said true
  exactly when the position is non-origin, but a bare positional '0' decodes to a non-null
  anchor and reports true. Now "decodes to a position other than the origin", matching the
  docblock.

No code changes — CHANGELOG.md only.

Verification

#	Gate	Method	Result
1	Content	Reread [Unreleased], [0.2.0], and the link refs	[Unreleased] holds only Planned; compare/v0.1.0...v0.2.0 ref already in place
2	Claim check	git log v0.1.0 --stat -- src/Offset	Path does not exist at v0.1.0, confirming no released build could hit the overflow
3	CI	The four required PHP legs	Markdown-only change; the suite must stay green regardless

Rollout

This unblocks the v0.2.0 release. Once merged: tag v0.2.0 at the merge commit, push the tag,
publish the GitHub release, and let Packagist pick it up (it currently serves v0.1.0 only).

Risk: 🟢 low — documentation only, no shipped code touched.

🤖 Generated with Claude Code