chore: add PR and issue templates

.github/ISSUE_TEMPLATE/bug_report.yml

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+name: Bug report
+description: Report something that isn't working as expected
+labels: ["bug"]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Thanks for filing a bug. Please attach a minimal PDF that reproduces
+        the issue where possible (redact sensitive content first) — most
+        pdfdebug bugs are hard to fix without a sample file.
+  - type: textarea
+    id: what-happened
+    attributes:
+      label: What happened?
+      description: A clear description of the bug — what you observed.
+      placeholder: When I opened this PDF and clicked …, the app …
+    validations:
+      required: true
+  - type: textarea
+    id: repro
+    attributes:
+      label: Steps to reproduce
+      description: Minimal steps so we can see it too.
+      placeholder: |
+        1. Open '...'
+        2. Click on '...'
+        3. See error
+    validations:
+      required: true
+  - type: textarea
+    id: expected
+    attributes:
+      label: Expected vs. actual
+      description: What you expected to happen, and what actually happened instead.
+    validations:
+      required: true
+  - type: dropdown
+    id: surface
+    attributes:
+      label: Where does this happen?
+      options:
+        - Desktop GUI
+        - CLI
+        - PDF parsing / inspection (pdfcore)
+        - Build / packaging
+        - Other
+    validations:
+      required: true
+  - type: input
+    id: version
+    attributes:
+      label: Version
+      description: pdfdebug version or commit — the release tag, or `pdfdebug --version`.
+      placeholder: v0.4.0
+    validations:
+      required: true
+  - type: textarea
+    id: context
+    attributes:
+      label: Anything else?
+      description: OS/platform, a sample PDF (redacted if needed), screenshots, or CLI output all help.
+    validations:
+      required: false

.github/ISSUE_TEMPLATE/config.yml

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+# Maintainers still file rich free-form issues — keep the blank option.
+blank_issues_enabled: true
+contact_links:
+  - name: Report a security vulnerability
+    url: mailto:security@unidoc.io
+    about: Do NOT open a public issue for security problems. Email security@unidoc.io directly.

.github/ISSUE_TEMPLATE/feature_request.yml

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+name: Feature request
+description: Suggest an improvement or a new capability
+labels: ["enhancement"]
+body:
+  - type: textarea
+    id: problem
+    attributes:
+      label: Problem / motivation
+      description: What are you trying to do, and what's getting in the way? Lead with the why, not the solution.
+    validations:
+      required: true
+  - type: textarea
+    id: solution
+    attributes:
+      label: Proposed solution
+      description: What you'd like to see happen.
+    validations:
+      required: true
+  - type: textarea
+    id: alternatives
+    attributes:
+      label: Alternatives considered
+      description: Other approaches you thought about, and why they fall short.
+    validations:
+      required: false

.github/pull_request_template.md

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+## Description and links
+
+<!-- What problem does this solve, and why. Link an issue if there is one. -->
+
+## Technical changes
+
+<!--
+Describe the changes at a high level, e.g.:
+1. Added a mutex around Inspector document access to fix a data race.
+2. Reworked ContentStreamViewer line splitting to handle CRLF.
+-->
+
+## Considerations
+
+<!-- Approaches you decided not to take, or anything you learned along the way. Optional for small fixes. -->
+
+## How was this tested?
+
+<!--
+- go test ./...
+- frontend: npm run test --prefix frontend
+- Manual: what did you click/run to confirm the fix?
+-->
+
+## What could go wrong?
+
+<!-- What could break, or what assumptions might be false? Optional for small fixes. -->
+
+## Screenshots/videos (if appropriate)
+
+## Checklist
+
+- [ ] Tests pass locally
+- [ ] I targeted the `dev` branch, not `master`