docs: drop ASCII architecture diagrams in favor of arch.png

ASCII renders unevenly outside monospace contexts (mobile reddit, weibo,
zhihu, twitter). The PNG was already next to each ASCII block; keeping
both was redundant and the ASCII added noise on mobile.

SPEC.md keeps its ASCII frame layout (intended for technical reference
in monospace contexts). twitter.md em-dashes are inline punctuation, not
diagrams; left untouched.

Author: WaylandYang

.github/announce/reddit_localllama.md

@@ -56,13 +56,12 @@ local LLM, cheap hardware, no cloud, MCP-compatible.
 
 ## What's on the wire
 
-```
-LLM ── MCP ──▶ Bridge (asyncio)  ── 19B wire frame ──▶ ESP32
-                 │
-                 ├─ capability token (HMAC-SHA256, scoped, expiring)
-                 ├─ range / type / unit check from manifest
-                 └─ dry-run as a wire-format bit (kind=0x81)
-```
+![DCP architecture: LLM ↔ MCP ↔ Bridge ↔ DCP wire ↔ Device](https://raw.githubusercontent.com/device-context-protocol/dcp/main/docs/paper/figures/arch.png)
+
+The Bridge is the sole trust boundary. On every call it verifies the
+capability token (HMAC-SHA256, scoped, expiring), checks range/type/unit
+against the manifest, and supports dry-run as a wire-format bit
+(kind=0x81). Devices never see a byte that hasn't been screened.
 
 Wire frame: 6-byte fixed header + CBOR map + optional 16-byte HMAC.
 A `set_brightness(50)` call is 19 bytes. MCP JSON-RPC equivalent

.github/announce/zhihu.md

@@ -33,15 +33,9 @@ DCP 把 LLM 安全相关的几件事直接做进了**协议层**,不是 applicat
 
 ### 架构
 
-```
-LLM ── MCP ──▶ Bridge(唯一可信边界)── DCP wire ──▶ Device
-                 │
-                 ├─ 容量 token 校验
-                 ├─ 范围/类型检查
-                 └─ dry-run 预演
-```
+![DCP 架构图](https://raw.githubusercontent.com/device-context-protocol/dcp/main/docs/paper/figures/arch.png)
 
-Bridge 是个 Python 进程,你的 LLM(Claude/本地模型/其他)说 MCP,Bridge 翻译成 DCP 喊设备。**设备永远收不到 LLM 直发的命令**。
+Bridge 是个 Python 进程,你的 LLM(Claude / 本地模型 / 其他)说 MCP,Bridge 翻译成 DCP 喊设备。Bridge 在每次调用前校验 capability token、范围/类型/单位、支持 dry-run 预演。**设备永远收不到 LLM 直发的命令**。
 
 ### 现在能做什么
 

README.md

@@ -56,17 +56,12 @@ out of the box. DCP is the last mile to physical hardware.
 
 ![DCP architecture](docs/paper/figures/arch.png)
 
-```
-LLM ── MCP ──▶ Bridge ── DCP wire ──▶ Device(s)
-                 │
-                 ├─ issues capability tokens
-                 ├─ enforces rate limits, ranges
-                 └─ logs, dry-runs, undo
-```
-
-The Bridge is the sole trust boundary. Devices remain simple enough to
-fit on commodity microcontrollers; everything the LLM is allowed to do
-is enforced before any byte traverses the device boundary.
+The Bridge is the sole trust boundary. On every call it issues and
+verifies capability tokens, enforces range/type/unit checks from the
+manifest, and supports dry-run as a wire-format primitive. Devices
+remain simple enough to fit on commodity microcontrollers; everything
+the LLM is allowed to do is enforced before any byte traverses the
+device boundary.
 
 ## Validated on real hardware