fix(location): confirm before sharing, with accuracy and an approximate option (#340)

The composer's location button sent the exact position (6 decimals) from a
single click once the browser permission had been granted, discarding the
fix's accuracy, so a ±3.5 km Wi-Fi/IP fix was shown as exact.

- ShareLocationDialog: "Share your location?" with the coordinates and
  ±accuracy, a "Check on OpenStreetMap" link, and Cancel / Send
  approximate (~1 km) / Send. Focus starts on Cancel; Esc cancels.
- utils/geoShare.ts (unit-tested): RFC 5870 geo URI with `;u=` accuracy;
  approximate shares round to 2 decimals and never claim better than 1 km.
- Location cards show the ± when the event carries `u=`.
- The toolbar icon is a pin instead of the globe.

Verified headless (fix 40.748817,-73.985428 ±3500 m): the click opens the
dialog and sends nothing; Cancel/Esc send nothing; Send approximate →
geo:40.75,-73.99;u=3500; Send → geo:40.748817,-73.985428;u=3500; the card
reads "40.74882, -73.98543 (±3.5 km)".

Fixes #340

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/app/components/message/MsgTypeRenderers.tsx

@@ -37,6 +37,7 @@ import {
 } from '../../../types/matrix/common';
 import { FALLBACK_MIMETYPE, getBlobSafeMimeType } from '../../utils/mimeTypes';
 import { parseGeoUri, scaleYDimension } from '../../utils/common';
+import { formatAccuracy } from '../../utils/geoShare';
 import { Attachment, AttachmentBox, AttachmentContent, AttachmentHeader } from './attachment';
 import { FileHeader, FileDownloadButton } from './FileHeader';
 
@@ -732,6 +733,8 @@ export function MLocation({ content }: MLocationProps) {
   const lon = parseFloat(location.longitude);
   if (!isFinite(lat) || !isFinite(lon)) return <BrokenContent />;
   const description = typeof msc3488?.description === 'string' ? msc3488.description : undefined;
+  // RFC 5870 `;u=` uncertainty (meters), sent by Lotus since Gitea #340.
+  const accuracyLabel = formatAccuracy(Number(/;u=([\d.]+)/.exec(geoUri)?.[1]));
   const mapSrc = `https://www.openstreetmap.org/export/embed.html?bbox=${lon - 0.007},${
     lat - 0.004
   },${lon + 0.007},${lat + 0.004}&layer=mapnik&marker=${lat},${lon}`;
@@ -772,6 +775,7 @@ export function MLocation({ content }: MLocationProps) {
       )}
       <Text size="T300" priority="300">
         {`${lat.toFixed(5)}, ${lon.toFixed(5)}`}
+        {accuracyLabel && ` (${accuracyLabel})`}
       </Text>
       <Button
         as="a"