chore: strip emoji and decorative glyphs from CLI output

[AlephNotation]

Why

Decorative glyphs in CLI output are out of place for a tool that wants to feel like infrastructure rather than a prototype. Survey of tools we want to be aesthetically adjacent to:

Tool	Emoji in output?
git, go, cargo, rustc, kubectl, terraform, docker, aws, gcloud, ripgrep, fd, bat	None
gh	Only ✓/✗ for check status, gated on isTTY() with ASCII fallback
npm	Used to, removed
yarn v1	Famously did, removed in v2/berry after backlash

Concrete reasons it's not just aesthetic:

• Breaks programmatic consumption. Anything piped through grep/awk/jq or parsed by another script has to deal with multi-byte clutter. The CI failure on fix(update): make "update available" nag actually print #188 was a clean example: TestRepoLifecycle couldn't find "v1" in vers repo tag list -q output because 💡 vers update available... was in the same buffer.
• Breaks alignment. Most emoji are East-Asian-Wide (2 cells) and ⚠️ is a 2-codepoint sequence (U+26A0 + VS-16) that renders as 1 or 2 cells depending on terminal/font, so any column-aligned output desyncs.
• Breaks on non-UTF-8 transports. Serial consoles, some SSH multiplexers, older Windows terminals, log shippers that re-encode — all turn emoji into ? or raw bytes.

What

Adopt the lowercase-prefix convention used by gcc/rustc/clippy/go:

Before	After	Notes
✓ <message>	<message>	drop — success implied by exit code 0
✗ <message>	error: <message>	lowercase compiler-style prefix
⚠️ <message>	warning: <message>
💡 <message>	note: <message>
📧 Verification email sent…	Verification email sent…	text is already explanatory
fmt.Println("✓")	fmt.Println("ok")	for "doing thing... ok" progress lines
fmt.Println("✗")	fmt.Println("failed")
├─ / └─ (commit lineage tree)	`	-/-`
→	->	everywhere — output strings, comments

Also lowercased the first character following the new prefixes (error: failed to delete ..., not error: Failed to delete ...) so it reads as one sentence, matching clippy/rustc/gcc exactly.

Scope and non-changes

• Pure output cleanup. No behavior changes, no flag changes, no API surface changes.
• 31 files touched, exactly +122/-122 lines (every replacement is 1:1).
• go build ./... && go vet ./... && go test ./... (unit) all pass.
• Box-drawing dividers in code comments (// ── Section ──) are left alone — they're cosmetic, never appear in output, and removing them is bikeshedding.
• The é in cmd/env_test.go test data ({"café", false}) is intentional non-ASCII test data and is left alone.

Followups not in this PR (worth a separate cleanup)

While auditing I noticed several places that print errors to stdout rather than stderr (e.g. internal/presenters/deletion_presenter.go:37). That's a real "treat this like a serious dev tool" defect — error output should not contaminate vers ... | jq style pipelines — but it's a behavior change, not a glyph swap, so it doesn't belong in this PR. Happy to do a follow-up.

Interaction with #188

This branches from main and is independent of #188. If #188 lands first, this needs a trivial rebase to also rewrite the 💡 in the new printUpdateBanner (which #188 already routes to stderr). If this lands first, #188 needs to use note: from the start in its banner. Either order works.