Projects: classes as entities, and the sidebar fits short windows

A project is a class with facts (description, status, kind, party,
dates, links, notes) in one project.set event behind the format
feature projects. Four tools (books.add_project, update_project,
projects, project); documents and decisions link to projects; B-37:
on-spec costs are expensed as incurred, repayment is revenue, and the
unrecovered cost is never below zero (Kani). Viewer: a Projects list
and a project page with its figures, by month and by account. The
sidebar measures its footer instead of reserving a fixed 172 px.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T3gXMVt7XJPi6ens1or9Dj

crates/ledger-gui/src/pages/documents.rs

@@ -371,6 +371,7 @@ pub fn subject_icon(s: Subject) -> &'static str {
         Subject::Account(_) => icon::TREE_STRUCTURE,
         Subject::Asset(_) => icon::PACKAGE,
         Subject::Party(_) => icon::ADDRESS_BOOK,
+        Subject::Project(_) => icon::BRIEFCASE,
         Subject::Invoice(_) | Subject::Bill(_) => icon::FILE_TEXT,
         Subject::Period(_) => icon::CALENDAR_BLANK,
         Subject::PayrollRun(_) => icon::USERS,