docs: replace static SVG with Mermaid diagram for Collector

Replaces the vague static SVG diagram in the Collector introduction with a
Mermaid flowchart that clearly shows the internal pipeline: Receivers ->
Processors (with chaining) -> Exporters, plus Connector feedback loop.

Updated across all three locales (en, ja, zh) with localized subgraph labels.
Deleted the now-unused otel-collector.svg asset.

Fixes #7278

Author: LoveChauhan-18

content/en/docs/collector/_index.md

@@ -8,8 +8,6 @@ cascade:
 weight: 270
 ---
 
-![OpenTelemetry Collector diagram with Jaeger, OTLP and Prometheus integration](img/otel-collector.svg)
-
 ## Introduction
 
 The OpenTelemetry Collector offers a vendor-agnostic implementation of how to
@@ -18,6 +16,37 @@ and maintain multiple agents/collectors. This works with improved scalability
 and supports open source observability data formats (e.g. Jaeger, Prometheus,
 Fluent Bit, etc.) sending to one or more open source or commercial backends.
 
+```mermaid
+flowchart LR
+  subgraph Collector ["OpenTelemetry Collector"]
+    direction LR
+    subgraph Receivers
+      R1(OTLP)
+      R2(Jaeger)
+      R3(Prometheus)
+    end
+
+    subgraph Processors
+      direction LR
+      P1[Memory Limiter] --> P2[Attributes] --> P3[Resource]
+    end
+
+    subgraph Exporters
+      E1[[OTLP]]
+      E2[[Prometheus]]
+    end
+
+    subgraph Connectors
+      C1{{Connector}}
+    end
+
+    Receivers --> P1
+    P3 --> Exporters
+    Exporters -.-> C1
+    C1 -.-> Receivers
+  end
+```
+
 ## Objectives
 
 - _Usability_: Reasonable default configuration, supports popular protocols,