docs: rename to Job Tracker and add architecture + lifecycle diagrams

- Renamed the H1 from 'Job Agent' to 'Job Tracker' to match the published
  repo name.
- Added two Mermaid diagrams up front under 'How it works':
  - Architecture diagram: Next.js (RSC + API) ↔ Postgres+pgvector ↔
    Claude CLI ↔ local embedder, with HNSW cosine retrieval and the
    storage/ folder for uploads + generated PDFs.
  - Lifecycle diagram: end-to-end flow from profile setup → application
    creation → auto-indexing → generation (CV / cover letter / interview
    prep / emails) → review with ATS scoring → approve → pipeline tracking
    with unified feed, contacts, and per-company research → outcome →
    feedback loop that reindexes positive outcomes for future RAG
    retrieval.

Both Gitea and GitHub render Mermaid natively in markdown.

README.md

@@ -1,4 +1,4 @@
-# Job Agent
+# Job Tracker
 
 **EN** — Personal job-application command center: full-pipeline tracking, AI-generated CVs/cover letters/emails, per-company research log, recruiter networking, and an integrated event feed for every application. Postgres + pgvector RAG, Next.js 16.
 
@@ -6,6 +6,86 @@
 
 ---
 
+## How it works
+
+### Architecture
+
+```mermaid
+flowchart LR
+    User([👤 User])
+
+    subgraph App["Next.js 16 (App Router + RSC)"]
+        UI[Pages /applications /contacts /profile<br/>dashboard, raio-x, settings]
+        API[API routes<br/>async route handlers]
+    end
+
+    subgraph Storage["Persistence"]
+        PG[(Postgres 16<br/>+ pgvector)]
+        FS[storage/uploads<br/>storage/generated]
+    end
+
+    subgraph AI["AI subsystems"]
+        Claude[Claude CLI<br/>subprocess]
+        Embedder[Local embedder<br/>all-MiniLM-L6-v2<br/>384 dims]
+    end
+
+    User -->|HTTPS| UI
+    UI -->|fetch| API
+    API <-->|Drizzle ORM<br/>postgres-js| PG
+    API -->|stdin/stdout| Claude
+    API -->|index on write| Embedder
+    Embedder -->|vector embeddings| PG
+    API -->|PDFs, uploaded docs| FS
+    PG -.->|HNSW cosine `<=>`<br/>top-K chunks| API
+```
+
+### Lifecycle of one job application
+
+```mermaid
+flowchart TD
+    P([Set up profile<br/>experience, skills, documents])
+    A[Add application<br/>+ paste job description]
+    I[Auto-index JD chunks<br/>into pgvector]
+    G{Generate document?}
+    CV[CV<br/>profile + RAG + ATS keywords → Claude]
+    CL[Cover letter<br/>profile + RAG → Claude]
+    PR[Interview prep<br/>STAR answers]
+    EM[Email<br/>follow-up / thank-you / withdraw]
+    R[Review + ATS score]
+    F{Refine?}
+    AP[Approve]
+    K[Index approved CV/CL<br/>for future RAG retrieval]
+    T[Track pipeline status]
+    FD[Unified feed<br/>notes · stages · contact interactions]
+    CO[Link contacts<br/>recruiter, interviewer, hiring manager]
+    RES[Per-company research<br/>news · culture · glassdoor · tech stack]
+    OUT([Outcome:<br/>interview · offer · rejected])
+    LOOP[Feedback loop<br/>positive outcomes reindex<br/>improving future generations]
+
+    P --> A
+    A --> I
+    I --> G
+    G --> CV
+    G --> CL
+    G --> PR
+    G --> EM
+    CV --> R
+    CL --> R
+    R --> F
+    F -->|yes, with feedback| G
+    F -->|no| AP
+    AP --> K
+    AP --> T
+    T --> FD
+    T --> CO
+    T --> RES
+    T --> OUT
+    OUT --> LOOP
+    LOOP --> I
+```
+
+---
+
 ## Table of contents
 
 - [Features](#features)