Add core modules, web frontend, CLI, keystore, and fieldkit

Core:
- paths.py: centralized ~/.soosef/ path constants
- config.py: JSON config loader with dataclass defaults
- exceptions.py: SoosefError hierarchy
- cli.py: unified Click CLI wrapping stegasoo + verisoo + native commands

Keystore:
- manager.py: unified key management (Ed25519 identity + channel keys)
- models.py: IdentityInfo, KeystoreStatus dataclasses
- export.py: encrypted key bundle export/import for USB transfer

Fieldkit:
- killswitch.py: ordered emergency data destruction (keys first)
- deadman.py: dead man's switch with check-in timer
- tamper.py: SHA-256 file integrity baseline + checking
- usb_monitor.py: pyudev USB whitelist enforcement
- geofence.py: haversine-based GPS boundary checking

Web frontend (Flask app factory + blueprints):
- app.py: create_app() factory with context processor
- blueprints: stego, attest, fieldkit, keys, admin
- templates: base.html (dark theme, unified nav), dashboard, all section pages
- static: CSS, favicon

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontends/web/templates/stego/decode.html

@@ -0,0 +1,10 @@
+{% extends "base.html" %}
+{% block title %}Decode — SooSeF{% endblock %}
+{% block content %}
+<h2><i class="bi bi-unlock me-2"></i>Decode Message</h2>
+<p class="text-muted">Extract a hidden message from a stego image.</p>
+<div class="alert alert-info">
+    <i class="bi bi-info-circle me-2"></i>
+    Stegasoo decode UI will be migrated here from stegasoo's frontends/web/.
+</div>
+{% endblock %}

frontends/web/templates/stego/encode.html

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+{% extends "base.html" %}
+{% block title %}Encode — SooSeF{% endblock %}
+{% block content %}
+<h2><i class="bi bi-lock me-2"></i>Encode Message</h2>
+<p class="text-muted">Hide an encrypted message in an image or audio file.</p>
+<div class="alert alert-info">
+    <i class="bi bi-info-circle me-2"></i>
+    Stegasoo encode UI will be migrated here from stegasoo's frontends/web/.
+    Full hybrid auth (photo + passphrase + PIN) with async progress tracking.
+</div>
+{% endblock %}

frontends/web/templates/stego/generate.html

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+{% extends "base.html" %}
+{% block title %}Generate — SooSeF{% endblock %}
+{% block content %}
+<h2><i class="bi bi-key me-2"></i>Generate Credentials</h2>
+<p class="text-muted">Generate secure passphrases, PINs, and RSA key pairs.</p>
+<div class="alert alert-info">
+    <i class="bi bi-info-circle me-2"></i>
+    Stegasoo credential generator UI will be migrated here.
+</div>
+{% endblock %}

frontends/web/templates/stego/tools.html

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+{% extends "base.html" %}
+{% block title %}Tools — SooSeF{% endblock %}
+{% block content %}
+<h2><i class="bi bi-tools me-2"></i>Tools</h2>
+<p class="text-muted">Image analysis, capacity checking, EXIF stripping, and more.</p>
+<div class="alert alert-info">
+    <i class="bi bi-info-circle me-2"></i>
+    Stegasoo tools UI will be migrated here.
+</div>
+{% endblock %}