release: v0.6.3 — the things a new user hits first

[vyncint]

What & why

A review of mossaic from the outside — install, run, read what it prints — and
the fixes for what that found. Everything here is on a path somebody meets in
the first minute of using it.

The one shipped template warned on every year

$ mossaic-art --template dragon --year 2027
note: 6 cell(s) fell outside 2027 and were dropped — the first and last
      calendar columns are partial weeks

2025 through 2029, every one. And all six cells were blank margin —
dragon.art is 0 at both ends of all seven rows, so nothing was lost.
Canvas::place counted every cell that fell outside the year rather than every
cell that would have been drawn. It now counts only lit ones, so the note
appears when a shade is genuinely lost and stays quiet otherwise.

Counts did not read as English

Twenty-nine of them — 1 template(s), 6 cell(s), 59 day(s) — on the first
line of --list-templates and in the markdown the GitHub Action posts to a pull
request. plural takes both forms rather than appending an s, so verbs agree
too (1 day is short, 2 days are short) and the number's own formatting —
widths, thousands separators — stays at the call site where it belongs.

--help was thirty flags in a flat list

With a paragraph of colour theory inside --background. Now grouped: what to
draw, where it goes, tracking, making the commits, output — usage and
seven examples first. The colour theory moved to docs/ART.md, which already
had room to say it properly. 93 lines against 113, and no flag was dropped.

A missing --file in a script blamed the terminal

$ mossaic --file typo.json          # in CI
mossaic: needs an interactive terminal (No such device or address)

True, and no help in finding the typo. Only that case changed — with a terminal
the error is still shown in the chart with r to retry, which is the better
answer. My first attempt pre-checked the path and broke that; the existing PTY
test caught it, and the fix now sits at the point where the terminal is refused.

--font told its readers to edit src/art.rs

A note meant for contributors, printed to everyone who ran it.

And the catalogue is now a catalogue

--template NAME offered exactly one NAME. Three more ship: wave (one clean
sine across the year), pulse (a heartbeat trace) and invader. Each is 51
columns, so no lit day lands in a partial week, and each is drawn in {0, 2, 4}
— the only three of GitHub's greens that are all clearly distinct.

Two gates come with them, which matter now that #57 invites contributed art:

• every_template_reads_clearly measures the closest pair of shades in every
  template. Art using 2 and 3 looks obviously two-toned in the .art file,
  because the digits differ — and reads as one flat colour on github.com. Only
  measuring catches it.
• no_template_overhangs_the_year fails a template that loses a lit day off
  either end of any year.

Both were run against art planted to break them:

zz-faint: its closest pair is 2 and 3 at ΔE 11, which is not something
          a reader can rely on seeing
zz-faint loses 6 shades off 2026

Also

• The description never mentioned that mossaic is a terminal program, which is
  how it is found on crates.io. tui replaces contributions in the keywords —
  contribution-art already covers that ground.
• The action@v0.6.0 refs in docs/ and action/ had been stale for two
  releases. RELEASING.md §2b exists to catch this; it was not run.

Verification

• 213 tests, cargo fmt --check, clippy --all-targets --all-features -D warnings and RUSTDOCFLAGS=-D warnings cargo doc all clean.
• Every template drawn across 2026–2029: no warnings, none overhanging.
• Three new tests in tests/chart_cli.rs for the chart with no terminal —
  including the one that would have failed before this change.
• The --list-templates PTY test now reads full_text(): the catalogue
  outgrew one screenful, and "did this reach the terminal" is the question it
  was actually asking.

Checklist

• Tests added/updated for the change
• cargo fmt --all and cargo clippy --workspace --all-targets --all-features are clean
• All commits are signed off
• No AI attribution trailers
• CHANGELOG.md updated — released as [0.6.3]
• No snapshot changes