feat(install): style install.sh to match lipgloss CLI aesthetic

[ironystock]

Summary

Pure-ANSI hand-roll of `install.sh` so the `curl | sh` first-touch experience visually matches the rememberize CLI binary the user is about to run for the first time. Same rounded borders, same dim color-8 accents, same subdued green/red status glyphs as the lipgloss tables in `cmd/rememberize/render.go`.

Why not gum

Charmbracelet does ship `gum`, which exposes Bubble Tea / lipgloss components for shell scripts. But it's a separate binary — using it in install.sh would mean "install gum to install rememberize," exactly the kind of friction that defeats a one-line installer. Hand-rolled ANSI ships zero new deps on top of the `curl`/`wget`/`tar`/`unzip` the script already needs.

What it looks like

```
╭──────────────────────────────╮
│ Installing rememberize CLI │
╰──────────────────────────────╯

✓ Detected darwin/arm64
› Resolving latest release from github.com/captured-ventures/rememberize-cli...
✓ Version v0.1.0
› Downloading rememberize_0.1.0_darwin_arm64.tar.gz
✓ Downloaded
✓ Extracted
✓ Installed to /Users/brad/.local/bin/rememberize

Next steps

  Verify the install:
    rememberize --version

  Pair this machine to your rememberize account:
    rememberize pair <code>
    (get a code from https://rememberize.app/app/connections/new)

```

Opt-outs (any one suffices)

• stderr is not a TTY (piped to file, captured by CI, etc.)
• `NO_COLOR` env var is non-empty (https://no-color.org POSIX standard)
• `TERM=dumb`

In any of those cases the script falls back to ASCII glyphs (`[ok]`, `+--+`, `>`) and no colors — same content, just plain. The TTY check was confirmed locally — when run through a non-TTY stderr, output is the ASCII variant verbatim.

What's unchanged

• OS/arch detection, release-resolution, download/extract/install flow.
• PATH warning behavior.
• All exit codes.
• POSIX-sh compatibility (no bashisms).

Verification

• Local smoke (Bash via the agent — non-TTY, falls back to ASCII): script runs cleanly through to the version-resolve step (where it correctly fails because no `v0.1.0` release is published yet — that's Phase 5).
• Shellcheck-clean (verified before push).

Test plan

• CI green (`Test` jobs include shellcheck via golangci-lint? — actually no, shellcheck isn't wired in CI yet; consider as follow-up).
• Manual: run in a real terminal once `v0.1.0` is tagged: confirm rounded borders + green checks render.
• Manual: `NO_COLOR=1 sh install.sh` shows ASCII fallback.
• Manual: `sh install.sh 2>/tmp/install.log` (non-TTY stderr) writes ASCII to log.

Follow-ups (out of scope)

• Add `shellcheck` as a CI job for `install.sh`. Cheap, catches POSIX violations + common bash mistakes. Worth a small follow-up PR.
• The header-box width math is tied to the title string length. If the title ever has multibyte chars, `${#title}` will count bytes not display cells and the box will misalign. Fine for the current ASCII title; reconsider if we localize.

🤖 Generated with Claude Code

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