docs: structure update (#11275)

### **Restructure Docs Navigation & Consolidate Core Concepts**

**Summary**
This PR refactors the documentation navigation to follow a clearer
**User Journey** and consolidates fragmented pages to reduce redundancy.

**Key Changes**

* **Sidebar:**
* Replaced the legacy resource-based structure with user-journey-focused
categories.

**Proposed Structure:**

```
Get Started
├─ Overview
│   └─ Guides Overview (Brief intro to docs, persona-aligned: "Get auth working in minutes for your B2B app.")
├─ Quickstart Guide
│   └─ Quickstart (Step-by-step: Sign up, spin up instance, connect app, log in – mirrors brand's 4-step guide.)
├─ Authenticate Users
│   ├─ Login with ZITADEL (OIDC)
│   ├─ Get ID / Access Token
│   └─ Logout
├─ Examples & SDKs
│   ├─ SPA / Frontend
│   ├─ Web Applications
│   ├─ APIs / Backend Services
│   ├─ Hybrid / Full-Stack
│   └─ Sample Applications (Include community-contributed examples for openness.)
├─ Key Concepts
│   ├─ Instances, Orgs, Projects, Apps
│   ├─ Policies (Intro)
│   └─ Users & Roles
└─ Use Cases
    ├─ B2B Integration (Tailored to multi-tenant enterprise needs.)
    ├─ B2C Login
    ├─ Multi-Tenant / SaaS
    ├─ Branded Login & White-Label
    └─ Machine-to-Machine (M2M)

Configure Identity & Policies
├─ Identity Providers
│   ├─ External IDPs (e.g., Google, Azure)
│   └─ Custom Providers
├─ Policies
│   ├─ Password Policies
│   ├─ Lockout Policies
│   └─ Privacy Policies
├─ Roles & Permissions
│   ├─ RBAC Setup
│   └─ Custom Roles
└─ Compliance & Security
    ├─ Audits & Logs
    └─ Certifications (Highlight trust through openness.)

Integrate & Authenticate
├─ OIDC & OAuth Flows
├─ API Access
│   ├─ gRPC APIs
│   └─ REST APIs
├─ SDKs
│   ├─ Go
│   ├─ JavaScript/TypeScript
│   ├─ Python
│   └─ Others (Link to community SDKs.)
└─ External Integrations
    ├─ SAML
    ├─ LDAP
    └─ Webhooks

Test & Debug
├─ Testing Tools
│   ├─ Console Testing
│   └─ API Playground
├─ Common Issues
│   ├─ Token Errors
│   └─ Integration Failures
└─ Debugging Guides
    ├─ Logs & Monitoring
    └─ Error Codes Reference

Deploy & Operate
├─ Deployment Options
│   ├─ Cloud (ZITADEL Cloud)
│   ├─ Self-Hosted (Linux, MacOS)
│   ├─ Docker Compose
│   └─ Kubernetes
├─ Configuration
│   ├─ Environment Variables
│   └─ Advanced Settings
├─ Scaling & Performance
│   ├─ High Availability
│   └─ Backup & Restore
└─ Monitoring & Maintenance
    ├─ Metrics
    └─ Upgrades

Architecture & Concepts
├─ System Architecture
│   ├─ Core Components
│   └─ Data Flow Diagrams (Expressive visuals per brand.)
├─ Principles
│   ├─ Multi-Tenancy
│   └─ Open Standards (OIDC, SAML)
└─ Advanced Topics
    ├─ Customization
    └─ Extensibility (Open-source contributions.)

Product, Releases & Support
├─ Product Features
│   ├─ Roadmap (Public, for transparency.)
│   └─ Pricing & Tiers
├─ Releases
│   ├─ Changelog
│   └─ Upgrade Guides
└─ Support Resources
    ├─ Community (Discord, GitHub – for community-led growth.)
    ├─ FAQ
    ├─ Contact Support
    └─ Contribute (Encourage feedback/shaping the product.)
```

**Content Consolidation:**
* Merged separate "Concept" and "Console Guide" files into single,
comprehensive **Overview** pages for core resources:
* `Organizations`, `Projects`, `Applications`, `Users`, `Console`, and
`Actions`.

```
concepts/structure/organizations + guides/manage/console/organizations -> guides/manage/console/organizations-overview

concepts/structure/projects + guides/manage/console/projects -> guides/manage/console/projects-overview

concepts/structure/applications + guides/manage/console/applications -> guides/manage/console/applications-overview

concepts/structure/users + guides/manage/console/users -> guides/manage/console/users-overview

guides/manage/console/actions + apis/actions/introduction -> guides/manage/console/actions-overview

concepts/features/console + guides/manage/console/overview -> guides/manage/console/console-overview
```


**Redirects (`vercel.json`):**
* Added permanent redirects for all the 6 legacy files mentioned above



**No files were deleted**

---------

Co-authored-by: Florian Forster <[email protected]>

docs/docs/self-hosting/manage/cache.md

@@ -171,7 +171,7 @@ These settings typically change infrequently in production. ***Every*** request
 
 ### Milestones
 
-Milestones are used to track the administrator's progress in setting up their instance. Milestones are used to render *your next steps* in the [console](/docs/guides/manage/console/overview) landing page.
+Milestones are used to track the administrator's progress in setting up their instance. Milestones are used to render *your next steps* in the [console](/docs/guides/manage/console/console-overview) landing page.
 Milestones are reached upon the first time a certain action is performed. For example the first application created or the first human login. In order to push a "reached" event only once, ZITADEL must keep track of the current state of milestones by an eventstore query every time an eligible action is performed. This can cause an unwanted overhead on production servers, therefore they are cached.
 
 As an extra optimization, once all milestones are reached by the instance, an in-memory flag is set and the milestone state is never queried again from the database nor cache.
@@ -179,7 +179,7 @@ For single instance setups which fulfilled all milestone (*your next steps* in c
 
 ### Organization
 
-Most resources like users, project and applications are part of an [organization](/docs/concepts/structure/organizations). Therefore many parts of the ZITADEL logic search for an organization by ID or by their primary domain.
+Most resources like users, project and applications are part of an [organization](/docs/guides/manage/console/organizations-overview). Therefore many parts of the ZITADEL logic search for an organization by ID or by their primary domain.
 Organization objects are quite small and receive infrequent updates after they are created:
 
 - Change of organization name