#74 Diffs: per-file cards, dual line numbers, visual diffstat, drop mbox preamble

Commit detail and PR patch sections dump raw git show / git format-patch output into one <pre>. This is where GitHub/GitLab/Forgejo look most polished and we look like less.

Current

Commit page (commit/<sha>.html):

commit ec5b1f0bcaeacfd169d48a27bee83a414a639e46
Author: gl0w <gl0w@world>
Date:   Thu Sep 10 05:26:49 2026 +0100

    land #7 forge-readers + f0rge state

diff --git a/.forge/issues/f8c1…/issue.md b/.forge/issues/f8c1…/issue.md
index 2a46910..97d6ad7 100644
--- a/…
+++ b/…
@@ -1,13 +1,13 @@

PR page patch starts with the mbox preamble From 4eabe68… Mon Sep 17 00:00:00 2001, From:, Subject: [PATCH] …, then a text diffstat (src/commits.rs | 30 +++++…).

Problems:

1. No per-file grouping/cards — one giant block.
2. No line numbers (neither old nor new side).
3. diff --git / index / --- / +++ are colored with --diff-file, which equals --fg → visually indistinguishable from body text.
4. Hunk headers (@@ … @@) are plain; no function context emphasis.
5. Long paths wrap mid-token instead of scrolling per file.
6. Mbox/patch preamble is pure noise on the PR page.
7. Commit header (Author:, Date:) duplicates the meta shown above the diff.

Scope

• Emit one card per file: sticky file header (path, +n −m counts in green/red, "view file" link), collapse-all via <details open>.
• Two-column line numbers (old/new) in a gutter, --fg-dim, user-select:none, monospace alignment with the code lines.
• Diffstat bar: a real visual bar (green/red proportional divs) replacing ++++--- ASCII.
• Color ---/+++/diff --git with a distinct --diff-file token (not --fg), hunk headers --diff-hunk on a --surface-2 strip.
• Strip the From … mbox preamble and From:/Subject: lines on the PR page (they duplicate the PR title); keep the commit message body only.
• Per-file horizontal scroll (overflow-x:auto) instead of wrapping paths.
• Rust: commits.rs already emits diff-file/diff-hunk spans; extend to file boundaries + line numbers rather than re-parsing.

Acceptance

• every changed file renders as its own card with path + counts
• old/new line numbers align with code lines
• diff --git/---/+++ visibly distinct from code text
• PR patch has no mbox preamble
• no mid-token wrapping of long paths (scroll instead)