polish(pres_mgmt): consistent agree/consent modals + contrast + layout fixes

- Standardize all 3 consent modals (presenter × 2, session POC): same
  placement="top-center" size="lg", no custom height hacks, let Flowbite's
  native <dialog> handle scrolling; consistent footer Close button with X icon
- Modal titles now include person name; removes the double-header (inner <h2>
  in both form components was redundant with the modal title)
- Agreement text wrapper: bg-surface-100-900 → prose dark:prose-invert +
  bg-white dark:bg-gray-900 for proper dark-mode contrast on CMS HTML content
- Section/header bar changes color green when agreed (red when not), with
  check icon; "Change to not agreed?" button style aligned between both forms
- Remove pb-16 from pres_mgmt layout (leftover from defunct sticky action bar)
- Add @source for flowbite-svelte/dist so backdrop:bg-gray-900/50 is generated
  (modal backdrop dim was never active before — Tailwind wasn't scanning it)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app.css

@@ -46,6 +46,7 @@ html.light {
 @import './styles/ae-firefly-bgh.css';
 
 @source '../node_modules/@skeletonlabs/skeleton-svelte/dist';
+@source '../node_modules/flowbite-svelte/dist';
 
 /* Add your theme import for your theme: "osit-custom-theme" here */
 /* @plugin '@tailwindcss/forms'; */