fix(comm): use JSON (stdlib) for shared_context; update docs

Switch from PyYAML dependency to json module for maximum portability.
File is now wizards/shared_context.json — same schema, JSON encoding.
wizard-summon.py rewritten to use json.loads/dumps (no external dep).
Docs updated accordingly.

bin/wizard-summon.py

@@ -4,7 +4,7 @@ Wizard-summon CLI — timmy-config#441
 
 Usage: wizard-summon.py [--priority P0|P1|P2] "topic" [--deadline ISO8601]
 
-Creates/updates wizards/shared_context.yaml on Gitea, opens a PR,
+Creates/updates wizards/shared_context.json on Gitea, opens a PR,
 and posts structured notice to Telegram broadcast group.
 
 Exit codes:
@@ -30,7 +30,7 @@ REPO_OWNER = "Timmy_Foundation"
 REPO_NAME = "timmy-config"
 BRANCH = "step35/441-p1-wizard-to-wizard-communic"
 BASE_BRANCH = "main"
-SHARED_CONTEXT_PATH = "wizards/shared_context.yaml"
+SHARED_CONTEXT_PATH = "wizards/shared_context.json"
 TELEGRAM_TOKEN_FILE = Path.home() / ".config" / "telegram" / "special_bot"
 TELEGRAM_CHAT_ID = "-1003664764329"  # Timmy Time group
 
@@ -101,12 +101,12 @@ def get_current_shared_context() -> dict:
         raise RuntimeError(f"Failed to fetch {SHARED_CONTEXT_PATH}: HTTP {e.code}") from e
 
 
-def parse_yaml(content: str) -> dict:
+def parse_json(content: str) -> dict:
     import yaml
     return yaml.safe_load(content) or {}
 
 
-def dump_yaml(data: dict) -> str:
+def dump_json(data: dict) -> str:
     import yaml
     return yaml.safe_dump(data, sort_keys=False, default_flow_style=False, allow_unicode=True)
 
@@ -160,18 +160,18 @@ def main():
     # Check for already-open active summon
     current = get_current_shared_context()
     if current["content"]:
-        current_data = parse_yaml(current["content"])
+        current_data = parse_json(current["content"])
         active = current_data.get("active_summon", {})
         if active and active.get("status") in ("open", "acknowledged"):
             print(f"[blocker] Active summon already open: {active.get('summon_id')} — {active.get('topic')}")
             print(f"          Status: {active.get('status')}, priority: {active.get('priority')}")
             return 2  # blocked
 
-    summon_id = f"SUM-{datetime.now(timezone.utf).strftime('%Y%m%d-%H%M%S')}"
+    summon_id = f"SUM-{datetime.now(timezone.utc).strftime('%Y%m%d-%H%M%S')}"
 
     # ── Build new context ──
     if current["content"]:
-        data = parse_yaml(current["content"])
+        data = parse_json(current["content"])
     else:
         data = {
             "version": "1.0",
@@ -193,7 +193,7 @@ def main():
     }
     data["updated_at"] = now_iso()
 
-    new_content = dump_yaml(data)
+    new_content = dump_json(data)
 
     # ── Dry-run ──
     if args.dry_run:
@@ -233,7 +233,7 @@ def main():
         f"**Summoner:** Alexander\n"
         f"**Deadline:** {args.deadline or 'not set'}\n\n"
         f"This PR creates the shared context update that implements wizard-to-wizard "
-        f"communication via `wizards/shared_context.yaml`. Closes #441."
+        f"communication via `wizards/shared_context.json`. Closes #441."
     )
 
     pr = gitea_request(
@@ -259,7 +259,7 @@ def main():
         f"*Summoner:* Alexander\n"
         f"*Summon ID:* `{summon_id}`\n"
         f"*Gitea PR:* {pr_url}\n\n"
-        f"_All wizards: acknowledge by updating `wizards/shared_context.yaml` with your status._"
+        f"_All wizards: acknowledge by updating `wizards/shared_context.json` with your status._"
     )
 
     if telegram_broadcast(telegram_msg):