feat(output): modernize terminal output with a badges + rules design

[hahwul]

Summary

Modernizes jwt-hack's terminal output with a cohesive "badges + rules" design, without changing the stdout data/--json contract. All human-readable framing now flows through a single presentation layer.

What changed

• New design system — src/printing/theme.rs: section headers (▎ DECODE ────), sub-sections (▎ Header), dim-label/accent-value key-value rows, colored severity badges (● PASS / ▲ CRIT / ◆ MED / ■ LOW, and ✓ VALID / ✗ INVALID for jwks), a unified braille spinner and a block-fill progress bar (█▓░).
• Logger & banner (printing/mod.rs): dropped the [..] [..] bracket noise for a clean dim-time glyph message; compact dot-separated banner identity line.
• Per-command output restyled: decode, encode, version, payload, scan, jwks, crack.
• utils log_* + spinner helpers delegate to the theme.
• Latent bug fixed: width padding ({:<14}) was applied to already-colored strings, so columns drift under a real TTY (the pad counts ANSI escape bytes). Helpers now pad the plain text then color.

Before → After (decode)

  Algorithm     HS256              ▎ DECODE ─────────────────────────
  Type          JWT                  Algorithm     HS256
                            ──►       Type          JWT
  Header
  { ... }                          ▎ Header
                                     { ... }

Contracts preserved (verified)

• ✅ --json output byte-identical to main (machine path untouched; diffs only in pre-existing HashMap key-order + timing fields).
• ✅ Severity::as_str() / its Serialize impl and the HTML report unchanged — badges use a separate display method.
• ✅ stdout data lines (tokens, payloads, JSON, PEM) stay structurally intact & pipe-safe (encode | tail -1, payload | grep eyJ, decode | grep '"alg"').
• ✅ Color stays TTY / NO_COLOR gated via colored; badges remain glyph-distinguishable in monochrome (e.g. the shell TUI capture).

Verification

• cargo fmt --check, cargo clippy --all-targets, cargo build — all clean, zero warnings.
• cargo test — 434 passed / 0 failed (incl. new theme unit tests; verified race-free across repeated runs).
• Ran a multi-agent adversarial review over the diff; all confirmed findings (rustfmt, a flaky-test race, cross-command spacing, doc accuracy, jwks badge width) are fixed in this branch.

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

❌ Patch coverage is 57.86667% with 158 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/cmd/jwks.rs	0.00%	52 Missing ⚠️
src/cmd/crack.rs	6.66%	42 Missing ⚠️
src/printing/theme.rs	74.73%	24 Missing ⚠️
src/printing/mod.rs	0.00%	18 Missing ⚠️
src/cmd/scan.rs	61.76%	13 Missing ⚠️
src/utils/mod.rs	40.00%	6 Missing ⚠️
src/cmd/decode.rs	91.42%	3 Missing ⚠️

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