chore: cut the 0.8.0 release

[jamubc]

Why

The 0.8.0 work has all landed on main (PR #42), but the changelog still carries an ## [Unreleased] heading and is missing the Spaces-era entries. The release workflow reads the ## [0.8.0] section of CHANGELOG.md verbatim into both the GitHub release body and the in-app updater's "What's new" text, so the section must exist and be complete before the v0.8.0 tag is pushed.

What Changes

• Retitle the accumulated ## [Unreleased] notes as ## [0.8.0] - 2026-07-11, leaving an empty ## [Unreleased] heading on top, matching how every prior release was cut.
• Add the user-facing entries from the second half of the 0.7.0 to 0.8.0 history that were not yet recorded: Spaces, Revisit, time-section grouping, inline image paste/drop, the Links settings page, the resizable and collapsible sidebar, the About "Capture readiness" number, and the more dependable markdown preview.
• Internal-only commits (module splits, test additions, doc and CI chores) are deliberately omitted, per the changelog's "write it for users" rule.

MODIFIED Requirements

Requirement: the changelog drives release notes

The ## [0.8.0] section SHALL exist in CHANGELOG.md before the tag is pushed, and it MUST list every user-facing change since 0.7.0 in the existing Keep a Changelog format.

Scenario: cutting the release

• GIVEN the 0.8.0 work merged to main with notes still under ## [Unreleased]
• WHEN the release is cut
• THEN the section is retitled ## [0.8.0] - 2026-07-11, a fresh empty ## [Unreleased] remains on top, and the release workflow extracts the 0.8.0 notes into the GitHub release and the updater manifest

Verification

• The Build workflow passes on all three platforms (checks 3.1 macOS, Linux, Windows), confirming the changelog-only change does not break the gate.
• awk extraction against ## [0.8.0] returns the full section (the same logic release.yml runs), not the maintenance fallback.
• No em dashes and no AI attribution; authored as jamubc.