Rename the project to Instameex

Renames the app throughout: page titles, eyebrow/version labels,
Docker startup banner, main.py's header docstring, and the repo
links in the footer (now pointing at git.djeex.fr/Djeex/instameex
and github.com/Djeex/instameex, matching the renamed Gitea/GitHub
repos). Docker image and container are now named "instameex" too
(docker/compose.yaml), replacing the old instagram-hdr naming.

Adds the new logo: logo.svg is wired up as the favicon on both
pages, and logo-long.svg replaces the plain-text "Instameex" eyebrow
on the upload page as a properly sized wordmark.

The startup banner box width was recalculated by hand for the new
content (name plus Source:/Mirror: links instead of the old
license/upstream-credit lines), verified against a real container
rebuild so the border characters stay aligned.

kostis-kounadis/instagram-hdr-assembler references are left alone
throughout (README and banner): that's the separate upstream project
this app's gain-map logic is adapted from, not this app's own name.

README.md

@@ -1,8 +1,22 @@
+
+<div align="center">
+  <img src="src/assets/img/logo.svg" alt="Instameex logo" width="400"/>
+</div>
+<p/>
+<div align="center">
+<p>Mix your SDR and HDR exports into an Instagram-ready HDR photo.</p>
+</div>
+</p>
+<div align="center">
+  <img src="illustration/insta-hdr-1.png" alt="Instameex screenshot" />
+</div>
+
+
 > [!NOTE]
 > ⚠️ _This is an heavily vibe-coded proof of concept — **do not expose it to the internet** — use it at your own risk._
->  _Github repo is a mirror of https://git.djeex.fr/Djeex/insta-hdr-converter. You'll find full package, history and release note there._
+>  _Github repo is a mirror of https://git.djeex.fr/Djeex/instameex. You'll find full package, history and release note there._
 
-# Instagram HDR Assembler
+# Instameex
 
 A small web front end for assembling Instagram-compatible HDR JPEGs (gain
 map) from an SDR export and an HDR export out of Lightroom or Camera Raw.
@@ -13,9 +27,6 @@ itself based on the reverse-engineering work of
 [karachungen/instagram-hdr-converter](https://github.com/karachungen/instagram-hdr-converter).
 Original MIT license kept in [LICENSE](LICENSE). 
 
-
-![Instagram HDR Assembler screenshot](illustration/insta-hdr-1.png)
-
 ## How it works
 
 1. Upload an SDR file (`.jpg`/`.jpeg`) and an HDR file: either a gain-map