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-core/src/analysis.rs

@@ -148,11 +148,23 @@ pub fn pnl_by_interval(
     start: NaiveDate,
     end: NaiveDate,
     interval: Interval,
+) -> Result<Vec<IntervalPnl>, LedgerError> {
+    pnl_by_interval_for(ledger, start, end, interval, None)
+}
+
+/// [`pnl_by_interval`] for one class (project): only the lines tagged
+/// with it count (`None`: every line).
+pub fn pnl_by_interval_for(
+    ledger: &Ledger,
+    start: NaiveDate,
+    end: NaiveDate,
+    interval: Interval,
+    class: Option<crate::ClassId>,
 ) -> Result<Vec<IntervalPnl>, LedgerError> {
     intervals(start, end, interval)
         .into_iter()
         .map(|(s, e)| {
-            let pl = profit_and_loss_for_period(ledger, s, e, None)?;
+            let pl = profit_and_loss_for_period(ledger, s, e, class)?;
             Ok(IntervalPnl {
                 start: s,
                 end: e,