Rebrand SooSeF to FieldWitness

Complete project rebrand for better positioning in the press freedom
and digital security space. FieldWitness communicates both field
deployment and evidence testimony — appropriate for the target audience
of journalists, NGOs, and human rights organizations.

Rename mapping:
- soosef → fieldwitness (package, CLI, all imports)
- soosef.stegasoo → fieldwitness.stego
- soosef.verisoo → fieldwitness.attest
- ~/.soosef/ → ~/.fwmetadata/ (innocuous data dir name)
- SOOSEF_DATA_DIR → FIELDWITNESS_DATA_DIR
- SoosefConfig → FieldWitnessConfig
- SoosefError → FieldWitnessError

Also includes:
- License switch from MIT to GPL-3.0
- C2PA bridge module (Phase 0-2 MVP): cert.py, export.py, vendor_assertions.py
- README repositioned to lead with provenance/federation, stego backgrounded
- Threat model skeleton at docs/security/threat-model.md
- Planning docs: docs/planning/c2pa-integration.md, docs/planning/gtm-feasibility.md

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

frontends/web/templates/setup_recovery.html

@@ -1,6 +1,6 @@
 {% extends "base.html" %}
 
-{% block title %}Recovery Key Setup - Stegasoo{% endblock %}
+{% block title %}Recovery Key Setup - Stego{% endblock %}
 
 {% block content %}
 <div class="row justify-content-center">
@@ -135,7 +135,7 @@ function copyToClipboard() {
 // Download as text file
 function downloadTextFile() {
     const key = document.getElementById('recoveryKey').value;
-    const content = `Stegasoo Recovery Key
+    const content = `Stego Recovery Key
 =====================
 
 ${key}
@@ -151,7 +151,7 @@ Generated: ${new Date().toISOString()}
     const url = URL.createObjectURL(blob);
     const a = document.createElement('a');
     a.href = url;
-    a.download = 'stegasoo-recovery-key.txt';
+    a.download = 'stego-recovery-key.txt';
     a.click();
     URL.revokeObjectURL(url);
 }
@@ -163,7 +163,7 @@ function downloadQRImage() {
 
     const a = document.createElement('a');
     a.href = img.src;
-    a.download = 'stegasoo-recovery-qr.png';
+    a.download = 'stego-recovery-qr.png';
     a.click();
 }