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>

deploy/config-presets/README.md

@@ -1,7 +1,7 @@
-# SooSeF Threat Level Configuration Presets
+# FieldWitness Threat Level Configuration Presets
 
 Select a preset based on your operational environment. Copy the appropriate
-JSON file to `~/.soosef/config.json` (or let the setup wizard choose one).
+JSON file to `~/.fwmetadata/config.json` (or let the setup wizard choose one).
 
 ## Presets
 
@@ -40,7 +40,7 @@ Specific journalist or org targeted by state actor (Pegasus-level).
 
 ```bash
 # Copy preset to config location
-cp deploy/config-presets/high-threat.json ~/.soosef/config.json
+cp deploy/config-presets/high-threat.json ~/.fwmetadata/config.json
 
-# Or via CLI (future: soosef init --threat-level high)
+# Or via CLI (future: fieldwitness init --threat-level high)
 ```