v0.7.0 release prep: dependencies, launch video, README for new users

[withrvr]

Everything main needs before v0.7.0 is published to crates.io and tagged: dependencies up to date, a new launch video recorded from 0.7.0, and a README written for new users.

Dependencies (9052dae)

• GitHub Actions (the open Dependabot PRs): actions/checkout v5 → v7 (chore(deps): bump actions/checkout from 5 to 7 #13), softprops/action-gh-release v2 → v3 (chore(deps): bump softprops/action-gh-release from 2 to 3 #14), actions/upload-artifact v4 → v7 (chore(deps): bump actions/upload-artifact from 4 to 7 #15), actions/download-artifact v4 → v8 (chore(deps): bump actions/download-artifact from 4 to 8 #17).
• Cargo.lock: semver-compatible updates — serde_json 1.0.154, syn 3.0.8, cc 1.8.0, nix 0.31.3, mac_address 1.2.1. No direct dependency has a newer major/minor release.
• Not taken: chore(deps): bump dtolnay/rust-toolchain from 1.88 to 1.120 #16 (dtolnay/rust-toolchain 1.88 → 1.120): that tag is the Rust version the MSRV job installs, so bumping it would stop checking Rust 1.88. dependabot.yml now ignores that action. chore(deps): bump dtolnay/rust-toolchain from 1.88 to 1.120 #16 needs closing by hand.

Launch video (add7eba)

• New 23 s video (1920×1080, sound) made with /brag (/brag-slim). Every terminal frame is the real 0.7.0 release binary, recorded cell by cell: the menu, a 116 wpm run and its chart, missed words, the pace cursor, blind mode, Stats with nine real runs climbing, and the themes (four built-in + a custom one).
• docs/brag/: brag.mp4, a 6.8 MB README GIF, poster, storyboard, share copy, and the pipeline in source/ with rebuild steps.
• Removed the old v0.2 video and the assets/ demo media; dropped the matching exclude entries from Cargo.toml.

Docs (e7d5f66)

• README rewritten as a marketing page for people new to terminals: what it is, one video, why you'll like it, new in 0.7, a step-by-step download for Windows / macOS / Linux (plus cargo install), the first keys, links out. No contributor material, no per-version notes, no diagrams (it's the crates.io page).
• CONTRIBUTING: ways to help without code, the full CI check list (MSRV + audit), a table of where each kind of doc lives.
• docs/RELEASE.md: replaces the v0.2–v0.4 checklists and the gh release create step (which would clash with release.yml) with the real flow: checks on main → cargo publish --dry-run → cargo publish → push the tag.
• README build badge is served by GitHub (b144322); the shields.io one showed as a broken image when that service timed out.
• CHANGELOG (0.7.0), LEARNINGS and ROADMAP note the release prep.

Dependabot #13, #14, #15, #17 (included) and #16 (declined) are closed with a link here.

Checks

• cargo fmt --check, cargo clippy -D warnings: clean; cargo test --all-targets --locked: 357 passed; cargo +1.88.0 check --locked: ok; cargo audit: no advisories.
• cargo package --list: no docs/, media or .github/; crate 254 KB.
• All relative links and anchors in the edited .md files resolve.
• Release binary, throwaway HOME: a finished run lands in stats.json, and --replay 1 loads the same words.

After merging

git checkout main && git pull → cargo publish --dry-run --locked → cargo publish --locked → git tag -a v0.7.0 -m "TypeRush v0.7.0" && git push origin v0.7.0 (see docs/RELEASE.md).

[withrvr]

Dependabot PRs handled by this PR (each closed with a link back here):

PR	Update	Outcome
#13	actions/checkout v5 → v7	✅ included
#14	softprops/action-gh-release v2 → v3	✅ included
#15	actions/upload-artifact v4 → v7	✅ included
#17	actions/download-artifact v4 → v8	✅ included
#16	dtolnay/rust-toolchain 1.88 → 1.120	⛔ not taken: 1.88 is the MSRV the CI job checks; dependabot.yml now ignores this action

Crate updates (serde_json, syn, cc, nix, mac_address) are in Cargo.lock here too; there was no open Dependabot PR for them. No Dependabot PRs are left open.