/today route + calendar grid for chronological note browsing

[unforced]

Why

Aaron enjoys journaling in a daily cadence but doesn't want Lens to impose a "daily notes" default. A chronological surface decoupled from the default /notes list is the right shape: opt-in view for temporal browsing, not the home page.

Scope

Two related features, either one PR or two:

/today route

• Shows notes created, updated, or due today (grouped by section)
• Section: "Created today", "Edited today", "Due today" (if we ever add due dates — skip section if empty)
• Quick-capture button prominent on this page (since "today" often means "capture something for today")
• Empty state: "Nothing yet today — start capturing."

/calendar route (calendar grid)

• Month grid. Each cell shows a small indicator per note created/edited on that day (dot per note, capped at N visible with "+X more").
• Click a day → /today?date=YYYY-MM-DD (reuses /today with a date param)
• Navigation: prev/next month, "today" jump button, keyboard arrows
• Works with any vault, no opinion about what "journaling" means — just surfaces temporal density

Tests

• /today shows notes grouped by created_at today
• /calendar renders cells with correct indicator counts
• Date param on /today filters correctly

Out of scope

• Due dates / scheduled notes (different feature — add to the list later if it earns a slot)
• Daily-note templates that auto-create a "Today" note (over-opinionated; users can build it themselves with templates feature later)
• Weekly / monthly review surfaces — distinct feature

Priority

Mid. Land after the organization fundamentals (#23, #24, #25) are in.