feat: multi-provider model support via majordomo (local Ollama, OpenAI-compatible, etc.)

Replace the hardcoded ollama.Cloud binding with majordomo's provider registry,
so Gadfly can target any backend majordomo supports without code changes.

- cmd/gadfly/model.go: resolveModel() — GADFLY_PROVIDER (default ollama-cloud)
  prefixes bare model ids; GADFLY_MODEL may be a full provider/model spec, alias,
  or failover chain (verbatim). GADFLY_BASE_URL constructs openai/ollama/anthropic/
  google directly at a custom endpoint (OpenAI-compatible + local/remote Ollama).
  GADFLY_API_KEY else the provider's standard env var. + buildSpec unit tests.
- run.sh: provider-aware key gate (local Ollama needs none); maps OLLAMA_CLOUD_API_KEY
  -> OLLAMA_API_KEY; provider/base-url/key inherited by the binary. Gadfly-branded comment.
- entrypoint.sh: GADFLY_MODELS alias for OLLAMA_REVIEW_MODELS; provider passthrough.
- examples + README: Models & providers section. Upfront: only the Ollama paths
  (local + OpenAI-compatible-against-Ollama) are tested; OpenAI/Anthropic/Google
  are wired via majordomo but UNTESTED (no spend).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scripts/run.sh

@@ -87,11 +87,21 @@ case "$PROVIDER" in
   ollama)
     # Agentic lane: hand off to the cmd/gadfly binary, which runs a tool-using
     # agent over the checked-out repo so it can verify findings instead of
-    # guessing from the diff. The workflow builds the binary and exports
-    # GADFLY_BIN + GADFLY_REPO_DIR; we fall back to sane defaults for a
-    # local run.
-    if [ -z "${OLLAMA_CLOUD_API_KEY:-}" ]; then
-      REVIEW="⚠️ \`OLLAMA_CLOUD_API_KEY\` is not configured; this reviewer was skipped."
+    # guessing from the diff. The reviewer is majordomo-powered, so GADFLY_PROVIDER
+    # selects the backend (default ollama-cloud); local Ollama, OpenAI, Anthropic,
+    # Google and OpenAI/Ollama-compatible endpoints all work — see the README.
+
+    # Back-compat: map the consumer's OLLAMA_CLOUD_API_KEY secret onto the
+    # OLLAMA_API_KEY env the ollama-cloud provider reads.
+    if [ -n "${OLLAMA_CLOUD_API_KEY:-}" ] && [ -z "${OLLAMA_API_KEY:-}" ]; then
+      export OLLAMA_API_KEY="$OLLAMA_CLOUD_API_KEY"
+    fi
+    GADFLY_PROVIDER_EFF="${GADFLY_PROVIDER:-ollama-cloud}"
+
+    # Only the default cloud provider strictly needs a key up front; local Ollama
+    # and other providers either need none or read their own standard env var.
+    if [ "$GADFLY_PROVIDER_EFF" = "ollama-cloud" ] && [ -z "${OLLAMA_API_KEY:-}" ] && [ -z "${GADFLY_API_KEY:-}" ]; then
+      REVIEW="⚠️ No Ollama Cloud key configured (set \`OLLAMA_CLOUD_API_KEY\`) and \`GADFLY_PROVIDER\` is the default \`ollama-cloud\`; this reviewer was skipped."
     else
       BIN="${GADFLY_BIN:-gadfly}"
       if ! command -v "$BIN" >/dev/null 2>&1 && [ ! -x "$BIN" ]; then
@@ -101,8 +111,9 @@ case "$PROVIDER" in
         DIFF_FILE="$(mktemp)"
         ERR_FILE="${DIFF_FILE}.err"
         printf '%s' "$FULL_DIFF" > "$DIFF_FILE"
+        # GADFLY_PROVIDER / GADFLY_BASE_URL / GADFLY_API_KEY and provider key
+        # envs (OPENAI_API_KEY, …) are inherited from the process environment.
         REVIEW="$(
-          OLLAMA_API_KEY="$OLLAMA_CLOUD_API_KEY" \
           GADFLY_MODEL="$MODEL" \
           GADFLY_REPO_DIR="$REPO_DIR" \
           GADFLY_DIFF_FILE="$DIFF_FILE" \
@@ -142,8 +153,8 @@ $(tail -c 1500 agy.err 2>/dev/null)
 esac
 
 # --- assemble comment -------------------------------------------------------
-COMMENT="$(printf '%s\n### 🔭 Adversarial review — `%s` (%s)\n\n%s\n\n<sub>Automated adversarial review. Advisory only — does not block merge.</sub>' \
-  "$MARKER" "$MODEL" "$PROVIDER" "$REVIEW")"
+COMMENT="$(printf '%s\n### 🪰 Gadfly review — `%s` (%s)\n\n%s\n\n<sub>Automated adversarial review by Gadfly. Advisory only — does not block merge.</sub>' \
+  "$MARKER" "$MODEL" "${GADFLY_PROVIDER_EFF:-$PROVIDER}" "$REVIEW")"
 POST_BODY="$(jq -n --arg b "$COMMENT" '{body:$b}')"
 
 # --- upsert by marker -------------------------------------------------------