docs: add CHANGELOG and programmatic API usage to README

[kitsuyui]

Summary

• Adds CHANGELOG.md following the Keep a Changelog format
• Adds a Programmatic API section to README.md documenting the server and cli namespaces exported from src/index.ts

Motivation

rendering-proxy is published as an npm package (version: 0.1.0) with dist/index.d.ts type definitions. The src/index.ts re-exports both server and cli namespaces, so consumers can import the library programmatically — but until now there was no example or reference for how to do so. Similarly, a package without a CHANGELOG makes it difficult for consumers to evaluate the impact of version updates.

Changes

• CHANGELOG.md: initial file anchored to 0.1.0; points to git log for full prior history
• README.md: new ## Programmatic API section documenting server.main, server.createServer, server.createHandler, cli.renderToStream, and cli.main with TypeScript examples

Verification

• biome check . passes (30 files, no issues)
• No TypeScript source files changed

Trade-offs

The CHANGELOG starts from 0.1.0 with a pointer to git log rather than back-filling every historical release; back-filling would be error-prone and the git log already captures that history accurately.

[github-actions]

Code Metrics Report

	main (1c1db53)	#1636 (feca1b5)	+/-
Coverage	87.5%	86.9%	-0.7%
Code to Test Ratio	1:0.5	1:0.5	+0.0
Test Execution Time	6s	7s	+1s

Details

  |                     | main (1c1db53) | #1636 (feca1b5) |  +/-  |
  |---------------------|----------------|-----------------|-------|
- | Coverage            |          87.5% |           86.9% | -0.7% |
  |   Files             |             11 |              11 |     0 |
  |   Lines             |            201 |             207 |    +6 |
+ |   Covered           |            176 |             180 |    +4 |
+ | Code to Test Ratio  |          1:0.5 |           1:0.5 |  +0.0 |
  |   Code              |           1591 |            1648 |   +57 |
+ |   Test              |            913 |             961 |   +48 |
- | Test Execution Time |             6s |              7s |   +1s |

Code coverage of files in pull request scope (79.1% → 76.9%)

Files	Coverage	+/-	Status
src/server/index.ts	76.9%	-2.3%	affected

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Reported by octocov