feat(web): update Elixir and Erlang logos with dark theme support

[thiagoesteves]

Summary

• Replace the Elixir logo with the official Elixir-lang drop (rendered from elixir-lang.github.com), stored as elixir.ico/elixir.png (light) and elixir-dark.ico/elixir-dark.png (lightness boosted +0.15 in HSL space)
• Regenerate the Erlang logo from the existing erlang-otp.png as erlang.ico (light) and erlang-dark.ico (dark "rlang" text recolored to bright red so the full logo reads on dark backgrounds)
• Add .elixir-logo and .erlang-logo CSS classes that swap the image source via content: url(...) based on [data-theme="dark"] and [data-theme="night"]
• Update system_bar.ex and application_card.ex to use the new classes instead of fixed src attributes
• Add .gitignore negation rules so elixir-dark.* and erlang-dark.ico are tracked despite the existing elixir-* / erlang-* digest patterns

Risk assessment

Impact: the system bar and application cards show crisper, official logos that remain visible on both light and dark themes. No functional change.

Blast radius: only apps/deployex_web static images, app.css, and the two LiveView components (system_bar, application_card). No business logic, no other apps touched.

Regression risk: low. The change is purely visual - image assets and CSS class swaps. No data flow, state, or config changes.

Rollback: revert this commit. The previous elixir.ico, elixir.png, and erlang.ico are restored from git history.

Test plan

• mix format --check-formatted on changed files
• mix credo --strict on changed files
• Start the server and verify the Elixir and Erlang logos render in the system bar on light theme
• Toggle to dark theme and verify the logos swap to the brighter variants
• Toggle to night theme and verify the same
• Verify the application cards show the correct logos for Elixir and Erlang apps

🤖 Generated with Devin (GLM-5.2 High)