refactor: rename the application package to docsgpt

The backend import package is now docsgpt, the name it will carry on PyPI;
application was far too generic to install into anyone's site-packages.
git mv plus a mechanical rewrite of every import, dotted string and path
reference: 734 Python files, the compose files, Dockerfile, workflows, docs,
setup scripts, devcontainer, k8s manifests, vscode config, pytest and coverage
config, .gitignore. Behaviour is unchanged.

Kept for one release:
- A top-level application package whose meta-path finder resolves
  application.x.y to the already-imported docsgpt.x.y object, so old imports
  and entry points (celery -A application.app.celery,
  uvicorn application.asgi:asgi_app) keep working with a FutureWarning.
- Celery registers every application.* task name as an alias of its
  docsgpt.* task on start-up, so messages queued by the previous release still
  run. The redbeat key prefix moves to redbeat:docsgpt:v2: so schedule entries
  the previous release wrote are left unread instead of firing twice.

The backend image builds from the repository root (docker build -f
docsgpt/Dockerfile .) so it can ship the alias package; a root .dockerignore
allow-lists docsgpt/ and application/ and keeps caches, local data, .env
files, the sample index files and the Dockerfile out. Compose and the image
workflows point at the new context.

docsgpt/agents/tools/think.py

@@ -0,0 +1,70 @@
+from docsgpt.agents.tools.base import Tool
+
+
+THINK_TOOL_ID = "think"
+
+THINK_TOOL_ENTRY = {
+    "name": "think",
+    "actions": [
+        {
+            "name": "reason",
+            "description": (
+                "Use this tool to think through your reasoning step by step "
+                "before deciding on your next action. Always reason before "
+                "searching or answering."
+            ),
+            "active": True,
+            "parameters": {
+                "properties": {
+                    "reasoning": {
+                        "type": "string",
+                        "description": "Your step-by-step reasoning and analysis",
+                        "filled_by_llm": True,
+                        "required": True,
+                    }
+                }
+            },
+        }
+    ],
+}
+
+
+class ThinkTool(Tool):
+    """Pseudo-tool that captures chain-of-thought reasoning.
+
+    Returns a short acknowledgment so the LLM can continue.
+    The reasoning content is captured in tool_call data for transparency.
+    """
+
+    internal = True
+
+    def __init__(self, config=None):
+        pass
+
+    def execute_action(self, action_name: str, **kwargs):
+        return "Continue."
+
+    def get_actions_metadata(self):
+        return [
+            {
+                "name": "reason",
+                "description": (
+                    "Use this tool to think through a complex step — analyze "
+                    "tool results, weigh options, or plan multi-step work — "
+                    "before taking your next action."
+                ),
+                "parameters": {
+                    "properties": {
+                        "reasoning": {
+                            "type": "string",
+                            "description": "Your step-by-step reasoning and analysis",
+                            "filled_by_llm": True,
+                            "required": True,
+                        }
+                    }
+                },
+            }
+        ]
+
+    def get_config_requirements(self):
+        return {}