refactor: distribute Acaua as a Docker image instead of a desktop app

Acaua is a collective SOC daemon consuming only Zeek log files, not a
single-user tool needing local hardware like its siblings. Drop the
Tauri desktop shell, installers and self-update entirely; the server
and its web dashboard ship as a container, updated by pulling a new
image tag.

Link against the official prebuilt libduckdb instead of compiling it
from source via the bundled feature, cutting image build time from
15+ minutes to about 3. Fix a real bug found along the way: as PID 1
in a container, the daemon ignored SIGTERM and was always killed
after the stop timeout; it now shuts down gracefully.

Also corrects the Pillar 1 beaconing score: the period estimate had a
harmonic alias (a perfectly periodic 4h series resolved to 600s), and
the old score formula flagged pure random traffic as suspicious
(p95 = 0.839 on Poisson noise). The new formula was validated against
300 samples per scenario.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VAyr8d7HuAdUGB6aA5xmDD

.gitignore

@@ -1,10 +1,6 @@
 # Build artifacts
 target/
-apps/gui/src-tauri/target/
-apps/gui/src-tauri/gen/
 node_modules/
-dist-gui/
-/acaua-v*
 *.rs.bk
 
 # Runtime data and local datasets
@@ -37,6 +33,3 @@ research/.ipynb_checkpoints/
 CLAUDE.md
 AGENTS.md
 GEMINI.md
-
-# Logo copied into the UI directory by the desktop build script
-/apps/gui/ui/logo.png