fix: bug: architect-run.sh existing-PR check builds malformed URL — ${FORGE_API}/repos/… duplicates the repos segment (#717)

Introduce FORGE_API_BASE (bare API root without repo path) in lib/env.sh
and lib/load-project.sh. Replace all cross-repo curl calls in
architect-run.sh that incorrectly used ${FORGE_API}/repos/${FORGE_OPS_REPO}
(which expanded to .../repos/owner/repo/repos/owner/ops-repo) with
${FORGE_API_BASE}/repos/${FORGE_OPS_REPO}.

Also fix a same-repo label URL that duplicated the repos segment.

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

lib/load-project.sh

@@ -97,7 +97,8 @@ done <<< "$_PROJECT_VARS"
 # FORGE_URL: TOML forge_url > existing FORGE_URL > default
 export FORGE_URL="${FORGE_URL:-http://localhost:3000}"
 if [ -n "$FORGE_REPO" ]; then
-  export FORGE_API="${FORGE_URL}/api/v1/repos/${FORGE_REPO}"
+  export FORGE_API_BASE="${FORGE_URL}/api/v1"
+  export FORGE_API="${FORGE_API_BASE}/repos/${FORGE_REPO}"
   export FORGE_WEB="${FORGE_URL}/${FORGE_REPO}"
   # Extract repo owner (first path segment of owner/repo)
   export FORGE_REPO_OWNER="${FORGE_REPO%%/*}"