fix(config): use namespace import for sander to bypass __esModule trap

Runtime warning in 3003d54's sander 0.5.1 -> 0.6.0 bump:

  12 main.production.html:183 Boostnote resets the invalid configuration.
  console.warn @ main.production.html:183
  get @ main.js:1268
  (anonymous) @ main.js:36190

Diagnosed: ConfigManager.get() at browser/main/lib/ConfigManager.js:182
catches an exception from RcParser.parse() and emits the warning.
RcParser.parse() at browser/lib/RcParser.js:9 calls
sander.existsSync(...) which now throws TypeError because
`sander.existsSync` resolved to undefined.

Root cause: sander 0.6.0 added
`Object.defineProperty(exports, '__esModule', { value: true })` at
the top of dist/sander.cjs.js. sander 0.5.1 did NOT have this flag.

Boostnote's RcParser used `import sander from 'sander'` — Babel 6
compiles this to `_interopRequireDefault(_sander)`:

  function _interopRequireDefault(obj) {
    return obj && obj.__esModule ? obj : { default: obj };
  }

For sander 0.5.1 (no __esModule flag): wraps -> `{ default: sander }`
-> _sander2.default.existsSync resolves to the whole sander module's
existsSync. Works.

For sander 0.6.0 (__esModule: true): returns obj as-is ->
_sander2.default looks up the `default` export, but sander 0.6.0
exposes only NAMED exports (appendFile, existsSync, readFileSync,
...) with no `default` property. _sander2.default is undefined.
TypeError: Cannot read property 'existsSync' of undefined.

Caught by ConfigManager's try/catch -> "Boostnote resets the invalid
configuration" warning. Fires repeatedly because main.js:36190 has a
`setInterval(() => ConfigManager.get(), 5 * 1000)` that re-runs every
5 seconds for theme refresh. After 60 seconds, 12 warnings stack up
in DevTools console.

Fix: switch to `import * as sander from 'sander'` (namespace import).
Babel 6 compiles this to `_interopRequireWildcard(_sander)` which
handles both ESM-flagged and bare CJS modules: when __esModule is
true, returns the namespace directly (preserving all named exports);
when false, builds a new object from enumerable own properties +
default. Either way, the resulting `sander` binding has working
existsSync / readFileSync / etc. methods.

Single-file fix at browser/lib/RcParser.js:2 — the only file in
browser/ that uses `import sander from 'sander'`. All other consumers
use `const sander = require('sander')` (CJS form, no Babel interop —
gets the raw module.exports namespace directly), which never hit
this trap.

Bundle compiles unchanged at 8.32 MB / 1141 modules. After this
commit, RcParser.parse() correctly reads .boostnoterc, the catch
block in ConfigManager.get() stops firing, and user customizations
in .boostnoterc are no longer silently dropped.

Sander 0.6.0 stays in place — the bump was correct; only the import
style in RcParser needed updating to match modern Babel interop rules.

Author: Evaggelos Balaskas

browser/lib/RcParser.js

@@ -1,5 +1,5 @@
 import path from 'path'
-import sander from 'sander'
+import * as sander from 'sander'
 
 const BOOSTNOTERC = '.boostnoterc'
 const homePath = global.process.env.HOME || global.process.env.USERPROFILE