feat: add tickstem/heartbeat and tickstem/uptime

[mike392]

Description

Adds two Go SDKs from the Tickstem developer infrastructure suite. The cron SDK (tickstem/cron) and email verification SDK (tickstem/verify) are already listed.

tickstem/heartbeat → Job Scheduler

• Repo: https://github.com/tickstem/heartbeat
• pkg.go.dev: https://pkg.go.dev/github.com/tickstem/heartbeat
• goreportcard: https://goreportcard.com/report/github.com/tickstem/heartbeat
• Dead-man's switch heartbeat monitoring: create a heartbeat, ping its URL after each job run, get alerted by email if pings stop arriving
• v1.0.0 tagged, MIT license, >85% test coverage

tickstem/uptime → DevOps Tools

• Repo: https://github.com/tickstem/uptime
• pkg.go.dev: https://pkg.go.dev/github.com/tickstem/uptime
• goreportcard: https://goreportcard.com/report/github.com/tickstem/uptime
• HTTP uptime monitoring with SSL expiry alerts and configurable response assertions (status code, response time, body)
• v1.0.0 tagged, MIT license, >85% test coverage

Checklist

• I have read the Contribution Guidelines
• Packages have been added alphabetically within their sections
• Each package has a SemVer tag (v1.0.0)
• Each package is listed on pkg.go.dev
• Each package has tests
• The description ends with a period

[github-actions]

Automated Quality Checks

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❌ Repo link: missing from PR body

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❌ **pkg.go.dev**: missing from PR body
  > **How to fix:** Add the following to your PR description:
  > ```
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PR Diff Validation

Content checks

✅ Files changed: only README.md
❌ Single item: 2 added, 0 removed (expected exactly 1 change per PR)

How to fix: Each PR should add, remove, or change only one package.
Please split this into separate PRs — one package per PR.
✅ Description: ends with punctuation
✅ Description tone: no promotional language detected
✅ Category size: Job Scheduler has 21 items
✅ Description: ends with punctuation
✅ Description tone: no promotional language detected
✅ Category size: DevOps Tools has 104 items

Warnings

⚠️ Link text: tickstem/heartbeat differs from repo name heartbeat

How to fix: The link text should be the exact project name.
If the project name really is tickstem/heartbeat, this is fine. Otherwise change it to: - [heartbeat](https://github.com/tickstem/heartbeat) - ...
⚠️ Link text: tickstem/uptime differs from repo name uptime
How to fix: The link text should be the exact project name.
If the project name really is tickstem/uptime, this is fine. Otherwise change it to: - [uptime](https://github.com/tickstem/uptime) - ...

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[mike392]

Closing to resubmit once repositories have sufficient history (5+ months required per contribution guidelines).