feat(v1.2.0): add start-here callout and refine risk guidance

[ikelaiah]

Summary

• Add a dismissible "Start here" callout under the page intro on both index.html and branch-map.html. Overview links to the Beginner Daily Path; branch map points at the create-from-commit flow. Dismissed state is stored in localStorage under git-map-start-here-dismissed.
• Soften git reset --soft HEAD~1 from danger to caution. A soft reset keeps your edits staged, so the previous danger framing was stronger than warranted. The note now also reminds users to avoid it on commits they have already shared.
• Replace the standalone git merge origin/<branch> recommendation in the diverged scenario with a git fetch + git merge origin/<branch> pair, and update the summary so the two-step path reads naturally next to rebase and merge.

Why

This release came out of a project review focused on first-load orientation and command accuracy. Beginners landing on the overview see a wide map and three control groups without a clear "start here" signpost, and the diverged scenario was suggesting a merge against a remote-tracking branch without the fetch that makes it work. The soft-reset risk tier was also miscalibrated against the existing caution tier used for similar reversible operations.

Changes

• src/data.js — reset-soft risk and note; diverged scenario next and summary.
• index.html, branch-map.html — new start-here aside; #daily-path anchor on the overview.
• src/styles.css — .start-here component styles.
• src/version.js — bumped to 1.2.0; added shared setupStartHere with localStorage persistence so both pages reuse the same behaviour.
• README.md, CHANGELOG.md — version badge, 1.2 intro paragraph, full 1.2.0 entry.

Test plan

• node scripts/validate.mjs passes.
• Load index.html in a fresh browser profile — callout appears under the intro, the link scrolls to the Beginner Daily Path, dismiss button hides it, and reload keeps it hidden.
• Load branch-map.html in the same profile — callout stays dismissed across both pages because they share the storage key.
• Clear localStorage and verify the callout reappears on next load.
• Open the overview, check the reset --soft card now shows the caution badge instead of danger, and the spotlight note mentions keeping edits staged.
• In Situation Solver, pick "Diverged" — the next steps list shows git pull --rebase, git pull --no-rebase, git fetch, git merge origin/<branch> in that order, and the summary mentions the fetch-then-merge option.
• Confirm the v1.2.0 label renders in the header of both pages.